How can you get your spouse to undress or sit on the porch with you etc. ?
Pickpocket her clothes before you marry, and she will never wear clothes.
Tested on the Xbox 360.
This is not really possible without mods.
There are a few different mods, but the most popular is probably Dudestias Multiple Marriages and Spouse Dressup.
Note that this comes in two varieties, 1.0.0 and 0.9.3; and I'm not entirely sure both versions do what you want.
Their behavior depends on the house they are in. Your spouse will never leave the cell in which they are housed, so they cannot for example join you outdoors unless you bring them along as a follower. (Which might be a bad idea, as many of them are weak.)
If you do bring them along as a follower, however, you have another option for undressing or redressing them, the UFO.
These mods, of course, require SKSE and benefit greatly from the a mod manager, like NMM.