1) Generally speaking, search keywords are the best -because you can target users based on the exact search queries they’re looking for. I would start out with exact and phrase match, and just start there for Search. Also, please look at the search term report, and negate any bad traffic. Then, I would start a remarketing campaign, targeting past site visitors with display ads.
2) I would set two conversion events, one for the lead, the other for the actual purchase. Then for bidding, maybe focus on leads to start, then you can focus on purchases.
Best of luck!