I noted your comment about still being agile.  I don't know how tall you are, but make sure you have enough room between the bottom of the layout and your head when suddenly sitting up in the bed.  The first couple times you sit up from a good sleep in that bed (forgetting the layout is there) and bang your head on the bottom of the layout you aren't going to be happy.  Have a friend do a little measuring for you.

Also, you don't have to use a N scale track plan.  Look at plans in other scales. See what features they have you would like to incorporate into your plan.   I'm modeling in N scale, but my track plan was designed for On30.  You have your room dimensions.  Photocopy some feature of plans you like.  Take scissors to those photocopies and start arranging those pieces where you would like to see them in the room.  You can draw in the connector tracks between the pieces.

Also, you have to figure out how you are coming and going in and out of the room.  Are you using duck under sections (another good place for a headache)?  Are you going to use lift outs or hinged sections?

Since you are young you might want to make this layout to be moveable without having to tear it up.  Build it in sections like modules.  All of us in our 50s can tell you that education and career relocations are in your future.  There is no pain like ripping up a layout that you didn't plan on moving for a move. You put a lot of effort into it!  Make sure your modules are the right size that you can get those out of the room, down the hall and out the front door.

Take a look at how N-Trak joins their modules for shows.  Many of those modules have been traveling to shows for years without track damage.

There is another layout called the Cat Mountain and Santa Fe by David Barrow.  Plans of it are on the Model Railroader site.  Its modular and the layout system is called dominoes. Cat mountain is modern too.  It might give you some ideas.  The track plan shows the module lines.

Den