Well Pat, that would be entirely up to you and what you want from one. An in-frame kit is a great first bike very cheap for what you get and can do with one. Go with a good dealer known for good customer support. Most especially for a first build. The down side is, it is not going to work well on a full suspension with out some serious modifications. A rack mount is a good choice for full suspension bike and simpler to install. But the price goes up for most of them. A weed whacker home built can be built for less then 100 bucks and will work on the bike you want to use. Is a great way to learn a great many things. They also have drawbacks.
Trust me, 30 is fast enough on a bike. Its not like a dirt bike. 35 feels like 50 on a bicycle.
My advice would be, look around, see what you can afford and would like. Look at pics and just take it all in. There is no rush.
Relax and enjoy. This part, is just part of the fun.