The shorter the boat the easier the loop but also the slower it is for surfing glassy waves.
Sometimes, but not always. It depends on the boat. The Jitsu, for example, I have found to surf more like a longer boat in terms of speed (and is remarkably well behaved going down river too), and a lot of that is due to the rocker design towards the rear.
Best thing is to try boats. I was in the market for a 2Fun, and I would still love to have one. But in the end an offer came up and I went for an out and out playboat, because despite not being a young gun, I found the idea of learning vertical and aerial moves tempting, while I am still physically able.