#1 - you can offer up to the max proposed trades with the same player as your league allows. For example, I continually have 5-6 proposed trades on the table. Always trying to work a deal to better my team.
#2 - if owners sit on a trade because they think it's "stupid", I'll assume they aren't involved in the league, cancel the trade myself and then offer my guys to another team. For example, I offered Jose Reyes to 2 teams, left the proposed trade up for 8 days (figure if they are on vacation they might have missed it). When they didn't respond, I opened talks with another owner. It all depends on the league your in and the guys you play with, I guess. I always send along an e-mail either before proposing a trade, or along with the proposal explaining my reasoning.