The pinging noise seems to be ever present, but it's a cheap kit, and I can't say I expected it, but I wasn't surprised.
Compression hasn't dropped in my cylinder so I am assuming everything is alright.
A 19, because the intake on the cylinder is 19mm x 15mm. A 21 is a little bit over kill unless you do some port work.
Speaking of which, I will be installing my 19 (from a 15 Bing) on Sunday, woo! I'll post results.