That is a tough question to answer simply!
The "densitity" depends on the shape of your layout, how much of it is straight alignment, how sharp are the curves, hox complex are the switch/crossings arrangment, etc. etc.
On straight you can go with one mast for 360 mm of track or even better for 500 mm of track , which makes it then look very prototypical.
For curves, the sharper the curve, the more mast you'll need.
**Very roughly** I'd suggest one mast per curved track unit .

I'd made a rough estimate based on the above, low-ball order the masts and wires , to avoid over ordering then when close to completion order the eventual fill-in materials.

I plan my layouts using Wintrack , which allows a more realistic calculation through their catenary planning system and builds your bill of materials in the process.
Still, it's never 100% accurate!

I use catenary with M track, analogue, and find that the connections on catenary are better (or perhaps my track is very battered).

Currently just one feeder mast on each track, these are loops roughly 3-4 metres in overall length. So around 8-10 metres worth of track. Of course things change when you start isolating sections etc.

I should probably double up but don't see the need.

buying new overhead wires and masts, there should be enough secure contacts all along your layout. so my opinion is 1 feeder masts, this of course depends on isolated sections, obviously you need extra feeder masts for these sections. the thickness of the wires should also minimize the voltage droppage on your layout.

regards.,

John

Hi,

I don't know your layout or your plan. But in many times the feeder masts you need for the signals are sufficient to supply the layout if they are also used to feed the layout.

Regards

Markus