Welcome to the Forum and the hobby. I will echo the pros and cons of going to N-scale. I have been in HO scale for years. Sure, I could get more N-scale stuff into a given area, but both aging eyes and some decrease in dexterity would take some of the enjoyment out of it. Yes, you can do some simple track plans on 4' x 8', which two separate continuous ovals, connected by turnouts. The outer loop could use 22-inch radius track and the inner loop either 18 or 15" R. You may also be able to find 20" R sectional track if Walthers is still selling the Shinohara sectional track.
The best suggestion is to visit you local hobby shop specializing in model railroading, or go online and find books on planning a model railroad and on basic DCC. The tighter curves will limit the choice of locomotives and rolling stock, but, depending on the era you model, there are quite a number of both diesel and steam locomotives that will handle those curves. You just won't be able to run a Big Boy or the more modern six-axle diesels. I started out years ago with DC, and built my present layout (which uses a 14' x 14' room) wired for DC, as most of my original locomotives were DC. When I decided to add sound, I switched to DCC, but kept the DC blocks and added a DCC power pack, with a toggle switch on the control panel to select which. (No way can I convert all the older stuff...timewise or moneywise). After trying several different DCC systems, I settled on the NCE Power Cab, as being flexible and, with booster, having enough power for any train lashup I want to run. I would suggest looking into whatever systems your local club might have for compatability sake, should you run some locomotives on their layout...although the engines themselves will generally work on most DCC systems.
Best of luck with your new hobby!