Howdy, J, and welcome aboard. I'm in HO scale but the basic concepts aren't much different in N scale. some older N scale engines can be converted to DCC reasonably easily and other just aren't worth the time and effort. I'd give the guys at Tony's Train Exchange (www.tonystrainexchange.com) and ask them about each of your engines. They are real experts and don't try to sell you decoders for things they know are going to be a real pain.
We have a member her named SpaceMouse (Chip) that has written a really good 5 minute beginner's guide. You can find it at http://www.chipengelmann.com/trains/...rsGuide01.html. It's well worth reading.
I think I can visualize your layout space. That's actually a pretty good size for an N scale layout. You have enough run that you could probably get up to a second level on a 2.5% grade with no helix although a loop on the lower section would ease the grade. I'd urge you to plan for this but build a single level layout first. Once you've got that under your belt, you can use your grade to build a second level. A two level layout looks good on paper but it greatly complicates the the track laying and scenery components of both levels.
I don't know what kind of rolling stock you have. Some of the early N scale rolling stock had grossly over sized details and just didn't look very good. They also have wheels with really deep flanges, which can foul finer scale track work and also don't look very good. If the car looks good to you, it can be changed out to Micro Train couplers and closer to scale wheel sets for about $10-$12, depending on what kind of deals you can get on couplers and wheels. Changing couplers and wheels is really not that difficult. If the freight cars just don't look very good, it's probably not worth the money or effort. Sell those off and use the money to buy better quality rolling stock.
The most important thing is to first get a good plan down on paper...or computer, as is normally done now. XtrkCAD is a really good free layout planning program available at http://sourceforge.net/project/showf...kage_id=167813. It will take a couple of hours to go through the tutorial but it's well worth the effort. You can then start laying out what you want to see on on your railroad and upload track plans here for suggestions. The worst thing, and the most tempting thing, is to start cutting lumber and get to work. I'd wager than about 99% of us did that for our first layout and it that's why most of us built a second...and third layout. Learn from our mistakes and make your first layout one you want to stay with. It will save you a lot of time, money, and frustration.
HO Scale Modeler