1) FCC license would be required. MotoTRBO isn't anything special, it's just one of many different types of radios used by businesses on the "business band" (not a legal term, just a layman's way of saying the frequencies available for typical businesses to have their two-way radios on). Be aware that you'll not only need a FCC license, but will need to have a frequency coordinator in your area to find one or more frequencies for your business to use. For a repeater, you'll need to have at least two, an input (user to repeater frequency) and an output (repeater to user frequency). The frequency or frequencies will need to be compatible with your radios so it's important that you select the proper one(s) that your radio(s) will operate on.
2) A repeater is often the most expensive part of the system. The hardware is generally the least expensive part (and that's not generally all that cheap!) since it's basically a one-time expense (be sure to include funds for the antenna, some high quality feedline, a tower climber to install things, etc. etc. etc.). You'll also need a good site for your repeater and antenna. There will typically be a monthly cost for renting the space on the tower for your antenna and space on the ground for your equipment. You'll also need to have some specialized insurance that meets the specifications spelled out in the lease for that space as well.
You may be better served by contracting with a local company that provides businesses with access to their system. Chances are you'll end up with better coverage for less cost, and have someone to complain to when things don't work as you expect. They'll also make sure that you are initially legal and remain legal, even with changing rules and regulations. Those "cheap used" radios will only take care of the easiest and least expensive part of a properly working radio system.
