just gone through it myself - build 85 is the latest.
Logically the US$84 / 50 quid option is the best as it will open up all the options for ever, that's what I went for, but if you have no intention of playing over the net, you can save some cash.
Installing the mods is easy once you have worked out how to get them, which I fell foul of. Once you have worked that bit out, the installation itself is pretty painless. here's where you get them http://isiforums.net/f/showthread.php/1396
there's not too much more than your list, so if you want loads of different stuff, at the moment you'll be a little disappointed. As for how long, well assuming you aren't a dunce like me and take hours and hours to work out where to get the mods, I reckon about an hour after you start the initial download and payment, if you do so by PayPal.
If you add the time to get the updated versions of the Renault 3.5 mod, I suppose two hours, I found that the downloads took between ten and tweny five minutes each, and I've got a 20Mbps line.
However, as all are quick to point out, it is a Beta, and I've had it for about a week and have found a fair number of issues, some minor, others a bit of a pain. I personally don't regret buying it, as I can see the potential, but anyone who steps out of the well developed games into this may be a touch disappointed