7.5' to 9' 4X or 5X leader should work fine with a floater. Go shorter if the stream is bushy.

Lots of folks like using thingamabobbers for indicators due to their light weight.

If you don't like using indicators, just use a big ginked up dry fly like a stimulator as you indicator. Run a nymph dropper off the hook bend of the dry. You'll end up catching fish on both flies doing this.