Nextbase are decent and cheap - currently using a 522GW as my old 512GW died ( after 5 years of near constant power cycles, pretty decent ) Although common mistake is for people to go for high res rather than high fps. You're gonna want a mix, I shoot mine at 1080p 120FPS which is plenty good enough- although its capable of 60fps at 4k, the file size is huge.
As for the mounting, I stuck it as close as I could behind the mirror so its not in my view when I drive, and counters the Exige's low ride height, to try and give a more complete picture of your surroundings. Your main issue is going to be powering it, and hiding the wires. All I did was use run the wire along the windscreen frame at top, using small bits of black tape to hide/hold it. From there, its down the A pillar, again using the tape. After the A pillar it gets messy unless you fancy taking the dash apart or removing trim like the side sills, so all I did was run it outside in the weather strip, and then back inside under the sill, behind the passenger seat and plugged into the cigarette lighter.
As I said, not tidy by any means, but also no loose wires, and it was quick/easy to do and check.