I think that having bidders sign up for a bidder's number will work the best. Some people will hesitate to bid against their friends. Having anonymous bidder's numbers will reduce that.
One thing I would suggest is to fill in the bid amounts on the silent auction items. this way the bidder's will make the correct bid increase increment, plus the bidder will spend less time in front of the item, giving other bidder's more chance to see and bid.
You could also have a Ebay type "Buy Now" block, meaning if they bid that amount, the bidding is over and that bidder wins. You have to estimate the value of the item, then add a percentage higher, i.e., value is $100, Buy Now amount is $125 or so.
As a professional auctioneer, I also announce the option of opening up the silent auction items that have last second competition to a "mini-live auction" so the clock does not end the bidding. There have been times that I have more than doubled the bid amounts using this technique.
We always have choice #1. We make an announcment, 10 minutes before the close of the auction and the crowd rushes in to see if anyone has outbid them.
Another option is to sell tickets, have the people write their names on them and they can drop a ticket or many tickets into a jar/box for each item that they wish to win. The winners are drawn randomly. A friends Womens Group always does it this way, and they thousands at each event.
