Instructional hours definitely count towards your totals. I instruct and examine part-time while working full-time for an airline and required written permission from my company. If you fly anywhere near 900 hrs/year for your lot, forget it (I only do 4-500 hours). I am also conscious of taking work from full-time FIs so I only tend to do skill tests and more advanced stuff (aeros, IMC etc.)....and teach the wife!
, however that will depend on the FTO you want to work for; some might welcome somebody willing to do trail lessons as full-time FIs get a bit brassed off with them.
As far as flight time limitations go, you can instruct for free (but don't, as you will piss a lot of people off) and fly privately although your company may place limitations on you in these areas.
Practically, although it may seem like a great idea just now you will find that, unless you are single or otherwise free of other commitments, after you have lost time to weather, aircraft going tech and students calling off, it is quite a hassle.