I don't have any practical advice on growing mushrooms as I've never done it myself, but I have researched the subject for some time out of a personal interest (edibles, mostly, though the skills themselves seem rather transferable regardless of the particular kind of mushroom you're intending to grow). From what I gather from lurking on the shroomery forums, grow kits themselves are a one time use item with a relatively high markup. Though it's not much of an investment if you just want to try it out, and the skill needed for growing that way is relatively low so it doesn't really involve much risk if you are just testing the waters. Otherwise I would just go with a spore syringe and sterilize mason jars of your own substrate. For the fruiting stage with a four tier mini greenhouse and a couple humidifiers you could grow a lot, likely more than you would need iirc. So you could grow a lot more that way and more inexpensively than you ever could with grow kits. But I would read these forums:
http://www.shroomery.org/forums/I also own these DVD's, they were really informative so I would recommend them:
http://www.mushroomvideos.com/Sorry I'm not much help in terms of any of your specific questions, but aside from the initial investment growing mushrooms seems fairly inexpensive (I intend to grow Lion's mane rather than buy it, myself), and aside from the need to maintain a sterile working environment I hear it is easier than ordinary horticulture, or certainly hydroponics. I think though that ultimately it's going to end up being another hobby, unless you can do it at least partially for its own sake, finding pleasure in the activity of growing itself, you may not want to keep up with it as much. So I would probably consider that before, say, investing in a pressure cooker.
Edited by umop 3pisdn, 06 September 2012 - 10:57 PM.
