An important consideration -
How often are you considering changing the track layout? Most places change it every couple of months or so - I run at SoCal Raceway and we change the layout every single week (unless laziness rules. . .
It's not too difficult to put a setup together, and if you're going to mail-order layouts, it will delay your setup.
Easiest thing to do - layout with some duct tape - just little strips - and drive it. See what you think.
Put some "elements" in that you think a track should have - a chicane, decreasing/increasing radius spiral turn, keyhole turn, hairpin, straightway, etc. Use these elements kinda like "legos" - plug them into different places in your track.
Then, drive it. See if it has a rhythm, a "feel" to it. You don't have to set it up, just put some duct tape or cones to mark some lanes and just "feel" the track.
It gives you a LOT of ownership of the track. Also, if you have two or three people doing it as a team, you can get a real good layout.
Just my opinion, but I think that laying out a track is really something that needs to be more individualized.