Hi. I'll say this for now: if, IF you mean your layout will be on a flat plywood board, make sure you include a pop-up or access hole in it to reach problems in the back. Or, have it free standing so as to be able to walk around it. Otherwise you'll have to attempt reaching from front to rear to fix a problem. In doing this though, be ready to hit things and break things under you.. Next, consider a 'point to point' track plan which forces you to turn engines and some cars on either a turntable, wye, or balloon track, to go back the other way at each end of the line..This is how the 1:1 scale does it..In turn creating more jobs to do, RR-wise. Or, make road a 'continual' where trains can keep running, non stop, but is not the way the 1:1 scale (other than trolley systems) does it..
With N you get more RR in the same allotted space as HO, but tougher to work on, eyesight wise. HO is heftier and larger, but easier to work on and has allot more parts, engine types, car types, structures and accessories available, simply because HO has been around allot longer than N. But only you can make that choice.
Finally: Are you going to run analog DC, or digital DCC, 'DCC ready', or, 'DCC/sound on board' ? if, IF you go DCC I'd personally recommend going NEC PowerCab for control. About $125-$150. Or, you might like Digitrax, others..
All the the best with your project, M