I am well established in the Marklin Z camp and have been enjoying that for some time now. I know nothing about Marklin HO equipment. Except that I expect high standards. I have a high roof living space in my home which would allow for a loop about 3' x 20' about 10' high. So it will require a short ladder to access and should be DCC controlled remotely, ideally via a cell phone like he Roco system, and very reliable. The track won't be visible, just the train circulating above the central fireplace and TV on the big beam type structure that crosses the room. Of course I'll want a train with all of the bells and whistles, a steam train with smoke capability, something like a BR86 pulling ERA III (short) cars. Just for fun and also because my wife thought that would be nice!
Since I love Marklin Z and my Insider Club membership keeps me well informed about both Z and HO products I though I would start here. First question is 2 vs 3 rail track? And second question is whether Marklin is the brand for this project, as opposed to Trix, or Roco, or? A penny for your thoughts!

OK great, a good start and yes, reliable ops will be a big deal with this project as regularly dragging the ladder out to give it a little nudge would be a PITA! It is very dusty here in CA, dusty and dry. This will be a bulletproof type layout designed to be vacuumed. A keep alive circuit and or a heavy flywheel in the loco is a good idea. I'll check out the Lux system. It will have to be a DCC loco though as the best part will be operating the myriad DCC sound and light features from my couch! Do 3 rail systems have special requirements for DCC operation? Or is the DCC information just sent via a rail? Now that I think of it is 3 rail a DC system? Does it just use the center rail and one of the outer rails for power? I don't really understand why there is a third rail.

Digital is never DC.
You can operate three-rail track with DC and you can operate two-rail with AC as long as you have appropriate locos.

Digital is bipolar, so the diode tricks from two-rail DC cannot be used with digital.

Digital two-rail and digital three-rail use the same controllers and the same decoders, only difference is a symmetric track layout (three-rail, centre rail and outer rails) or an asymmetric layout (two-rail, left and right rail).

Centre rail can become rusty. A dry environment is good to prevent that. Frequent operation keeps the rust away.

Marklin with three rail is probably as good as you will get without having to constantly reach the track and locos. However dust will collect and locos will stall from time to time. If it is just a loop with no turnouts etc then there is a good chance little attention will be required. As you already have a Z layout then you will know about Marklin quality. If you like Z then why not just stick with that.

Thank you all so much for your thorough and very helpful responses! This is for me the real beauty of forums, talking to mates about how to go about something is more fun for me than watching you tube videos or leafing through manuals and ad copy. That often makes me more confused!
I am happy to hear that a Marklin HO C Track system is reliable and robust, and not like a completely different animal like an old school Lionel AC system! Happy to hear that they can be operated via a "normal" DCC system. I really have a good grip now on how the track works. Oh and I'm not 70, yet, only 60! I'll just put on my basketball sneakers and jump up there if a train jumps the track ;) Where I live we certainly have dust but the rails don't tarnish, there is no rust issue really. A dust car and regular running should keep it serviceable for the most part, and an occasional vacuum.
I'll try to compare a 1 gauge Marklin to an HO but I would not consider smaller. And I'd like to have a longer train running up there. I included some pictures to give you all an idea of the scale. That surface is 29.5" wide. I intend to add a cornice molding that will give me enough width for the track. If I use R2 C track about 36" width should be enough as the center diameter would be 34.40". I hadn't considered a turnout but of course that could be used to store a second loco if I ever wanted to. But I have an ideal spot at the pass through to climb up and swap out trains comfortably. I could put a teardrop section off to the right of the main oval over the bedroon door and maybe have some fun with that. For scenery I'm thinking narrow wood strips with trees which set behind the track mostly but a section or two could be in front and have the train weave behind them, the old in and out! That's it really. Christmas lights in some of those trees of course! Removing the tree strips and train should leave nothing to be seen up there, although the track can remain.

The next item of business will be picking out a loco and command system. The Marklin starter sets are nice but may not come with the more impressive loco's I like, or larger radius curves. I'd like a BR64 2-6-2 or something with a tender. I don't know how large I can go with R2 curves or how limited I would be with R1 curves so I'll have to look into that. Generally I would like to avoid the smallest R1 curves since I don't need them, but I can't go larger than R2.
My requirement for a DCC command station is only that it be wireless and perhaps reasonably priced. I'm sure the Marklin CS3+ is a great device but I don't know if they make something simpler and wireless. I really like the Roco Z21. It looks like the perfect solution to control this train wirelessly from an iPad on the couch. There is even a lower spec z21 version that could do the job. That Roco is the reason I have not researched Marklin control products yet.

I have the same concerns as Cookee has but I suggest that you start by making a mockup of your intended train. HO on C-track stands just under 2.5 inch tall. Place the mockup (boxes or true scale printout etc) on the same distance from the edge as the tracks are going to be. Check what it looks like from where you want to watch it. You may want to raise the track an inch or two. The tracks are to be screwed down to something anyway.

If you want a lager scale in the Marklin family the tightest curves requires about 50 inch and then you will probably be restricted to very short/small engines.

In the US you have 3-rail O-Gauge like Atlas O27 and O31. Again the engines for those tracks are not for the big steamers. MTH have always had remote control for their system and the current decoder generation (PS3) understands DCC too. I think Lionel have starter sets with a simple remote control dedicated to the engine in the box.

Given the size of the entire loop I think a HO train will look better – if you can spot it.

Note. If you introduce turnouts it will have a huge impact on operational reliability.

Sounds like a nice plan. Just for your info, there are starter sets that have locos with all the extensive functions you would like.

If you are really keen on the silberlinge coaches with a steam loco, could I suggest Marklins BR23? It has all the advanced features, and prototypic ally was used extensively with the silberlinges all the way into the 1970,s

Cheers....

Mike

Hey Mike, the Marklin POP set also looks very nice, Silberlinge coaches are pretty classy but the POP coaches are a lot of fun. What loco would have pulled those? The BR23 again? Or the Class 03? And there are the Era III cars sets which are all short dark green cars. But I saw a picture of a German Crocodile pulling 15 of them. Pretty cool. But only if they are lighted internally.

Sounds good. I'll stick with steam and find coaches that work together. Funny you mentioned the BR141 as the last Z scale Marklin I got was an E41, nice loco in blue livery, but I gotta have a steam loco. Since it is a first train in HO for me I could save a lot starting with a set.