Hi Ian,
Welcome to the Forum and to this great hobby of ours.
As you can see many of us have different views, so take your time to think through a number of issues.
[These questions have grown for me as I progress in the hobby.]
Some answers may take time to determine and may change as you continue.
1) Time. More valuable than money IMHO. How much time do you have for your hobby?
2) Money. Making a budget isn't easy. We may not have great advice as we are addicted to the hobby.
3) Enjoyment. Do you like fixing things? Do you like running trains more? Do you like building buildings and landscaping?
Do you like working with wiring, or would you prefer things to run out of the box?
4) Purpose. For me it is also for my family and friends, and part of my art practice as an artist.
Its worthwhile asking yourself what your end goals are... without getting too serious and losing the fun of just trying things out.
For a modest financial investment you can also buy other good running locos converted to Digital on Ebay.
But its also great to have new stuff from a dealer straight out of the box with the Märklin guarantee.
Did you say you already have the MS2 or are you planning to buy one?
There are some really nice starter sets out there that work out much cheaper than pieces bit by bit together, since you are buying into a package deal.
They have MS2, C-track and a variety of really beautiful loco/train sets.
Then again there are some of us who love just running them fast.
Others, like myself, prefer them slow and running at "prototypical speeds" unless of course you have the Italian racing spirit and were raised riding in a Ferrari.
Or was it a Fiat, Baggio?

Once again, welcome and we will do our best to help you with your questions.
I have found the search feature on this forum very valuable.
Cheers,
Mark
Originally Posted by: baggio 
Having said that, I spent a lot of money having my old FS424 (no. 3035) and am very happy I did because of emotional attachment to it. It is now digitized and runs very well.
BUT, for about the same money (and maybe less), I could have bought a brand new loco with sound. Chances are, however, that the new loco would not be so fast as my Italian Stallion!

No Marklin loco is.