I have a few different answers for the first question, if you have a larger budget than I would say you should buy a nimbus unicycle, you should try to aim for around 20 inches, but a bit higher or lower is not that bad. The next option is what I would pick is the torker cx line, these are good sturdy cheap models, but without a doubt I would get a new seat for it immediately the one it comes with is condensed agony. I have the Kris Holmes fusion free ride saddle and that one is great for learning. You should probably buy two or more new saddle hand grabs, they go by pretty fast. Now your last option is if you want to buy one second hand, this fine, but keep in mind to research the manufacturer, and then see the retail prices, you can find some good deals but be sure to avoid companies like cyclepro and other stuff that gets bad reviews, if one unicycle by the manufacturer is bad than most of them are bad. But make sure to check. Don’t worry about the price on second hand places, most of the time people just get really mad at it and just want to get rid of it. Now, new if it’s too cheap retail (about under $50 is bad usually, but you can find good ones about this price even though it’s a good rule of thumb.). And remember; do not make your first unicycle your only one, EVER! They take a lot of wear and often don’t suit your needs. Now finally when you get to the buying stage, some good places to go are http://www.seriousjuggling.com/unicycles.htm http://www.unicycle.com/ (the first is the lower price range and the second is the higher.)