5x7 is just as fine as any size to start. It will most definitely be less expensive.
Dektol is fine. Ilford Multigrade would be another one. Kodak has some liquid concentrates that are fine too. It doesn't really matter all that much.
When I started printing, I followed Michael Smith's advice and printed one sheet knowingly too dark, another knowingly too light (takes a couple of sheets to figure out what too dark and too light is), and judge the work print exposure from that. After you get a good exposure, you select what grade you want to print at (sometimes you have to compensate for switching grades). I felt that this was a good method for learning to judge negatives before I print them.
Other people will probably advice you to make test strips, which is a fine method as well.
When you're comfortable making a decent work print, you can start experimenting with dodging and/or burning. For that I have used an opaque sheet of paper that is flexible; flexible so I can bend it and form round shapes along with having a straight edge. That's for burning.
As far as exposure to chemistry, I would say that as long as you wear nitrile gloves, have ventilation sucking the chemistry fumes away from you, while you have a fresh air intake in the other end of the room, creating a negative pressure above your chemistry trays, will help you a lot.
But I've never been pregnant, so I can of course not guarantee this use of ventilation...
Have fun! It's when the printing begins that photography comes full cycle, and the effects of different films and film developers become fully apparent.