3) The blind basket from 1st-line
is probably your best option. It works great for me, although it is a tiny bit loose in the portafilter.
4) My 57mm tamper is not extremely tight either. I've often read that a perfect seal makes no difference in espresso quality. Smaller tampers may allow you to use more types of baskets, as well. Truth be told, very few tampers are exactly their listed sizes, as documented in the HB Tamper Roadshow
. So yeah, it's normal.
5) I usually just run the boiler until it sputters as well. If I then run water through the group, there is almost no delay. Since the steam wand pulls from the top of the boiler, and the group head is downstream of the steam wand, I think it's fine. I can't imagine that covering another 2% of the heating element with liquid water would make a difference.