I really think you need to get out to a club a couple times before you buy anything. There are lots of choices and you'll be happier in the long run if you take some time wo weigh them all before buying. You can learn with either electric or glow.

A quick comment on terminology. Among people who fly, the internal combustion engines are usually called glow (alcohol/nitro based fuel), gas (larger planes running gasoline), and diesel (running some kind of diesel fuel). If you tell people at a flying field that you want to learn with a gas plane they'll think you want a really big trainer! It's unfortunate that the car crowd uses the term gas to refer to nitro engines, that's a bit confusing.

And finally about seaplanes. Yes, there are seaplanes and planes with floats. In fact, there's a whole forum here on RCU that's dedicated to seaplanes and float planes. I had one a while ago and I plan to build one or two more sometime soon. They are a huge amount of fun. Taking off and landing is a bit less forgiving than land, so they are not good to start with, but I'd say someone who has mastered (can fly it really well) a trainer would be ok installing floats on a stable high wing plane and flying off water.