As a long time N-scaler, I can honestly say I've never used Woodland Scenics foam inclines. But I've had a fair amount of experience with the pink and blue foam available at most box stores (although the variety and quantity available may vary in different parts of the country).
However, reading articles and seeing other layouts that have incorporated the foam inclines, looks to me like there's nothing wrong with them. They're an easy way to achieve inclines without all kinds of fancy and messy wood work required for other methods. As with the gluing of any foam, just make sure the glue or calk you choose is safe for foam. They will generally state on the container if so.
Depending on how far you wish to take scenery, you may want to get a sheet of pink or blue foam 1" thick or more and glue this first to your door. That would allow you to carve down into it for scenic effects such as creeks, rivers, gullys, ditches, etc. Otherwise, for a more simplistic approach, merely skip the 1" thick sheet of foam and do flatbed scenery.
Hopefully your door is 36" x 80". That would give you a really nice size for a layout. But 30" or 32" x 80" isn't bad either. Much smaller than 30" wide will start limiting the size of decent curve trackage with regards to a decent track plan.
Although 9-3/4" radius is the defacto-standard curved track included in virtually all N-scale starter sets, it will limit you to shorter 4-axle diesels and small steamers. If at all possible, try and do 11" radius minimum for all curve trackage and you will be much better off - most N-scale equipment runs much better at this minimum radius.
Do a search "N-scale hollow core door layouts" and see what pops up. You will undoubtedly get a lot of good results, as a lot of these door layouts have been built over the years.
Hope this helps. 
