learning from bag seeds can be a good idea provided you follow the advice given here - that is ....
1) Realize that you might not get any females or any smokable product
2) Use your first couple of grows as a learning experience and try not to get frustrated.
3) Use the experience you gain to get yourself set-up to do a bought-seed grow - meaning you'll already know what lights, nutes, ventilation do to/for plants so you'll be less likely to waste your bought seeds (and the money you spent on them).
4) your experience with bag seeds will carry over to the bought seeds - you'll be able to ask the "right" questions and you'll get the expert advice of others on the forum.
and since a lot depends on the strain - the plant from a bag seed should be just as good (if not better - depending on the grow conditions) as what you smoked! but (and this is a big but) if you have bag seeds, the weed obviously wasn't sinsemilla so you'll likely end up with hermaphrodites. But as long as you're doing this for experience (and maybe a toke or two) - you'll be fine with that, right?
as for ordering seeds, do it the "smart" way and you shouldn't have any issues. the "smart" way being - use cash and have them sent to a safe house (a house where nothing illegal is going on).
have patience, have fun and good luck!