I think you will find a lot of encouragement here about buying a Raodster to complement the Model S. That is exactly what I did [emoji3]
Going 100 Percent Electric | Tesla Motors
There are multiple existing threads covering your questions so I strongly recommend using site search or just browsing through the main Roadster forum and you will find many opinions. In my opinion the difference between the 1.5 / 2.0 / 2.5 cars are relatively minor. I am very happy with my 1.5 and it cost less than the later versions.
You need the latest firmware to use Henry's CAN SR adaptor to charge from your HPWC. See link shown below. The adaptor works very well and I recommend it, though Henry is careful to state that he cannot guarantee it to work on every single HPWC. Works great for me and many others!
Yes the 3.0 upgrade release is expected very soon (for all Roadsters as far as we know), I hope this month, see
Roadster 3.0 | Tesla Motors and
Roadster 3.0
Model S to Roadster adapter
Model S to Roadster adapter
Many people are happy with the standard factory soft top but some like the hardtop which is several thousand dollars so cars for sale with a hardtop tend to cost a bit more. This is an aftermarket Transparent Roadster Top
Transparent Roadster Top And some people rarely have any top on at all!
Discussion of changes to the Roadster over the years of production
Roadster History North America
Here is a discussion of why people ordered certain options or not
Necessary options
Good luck with your search for a Roadster! They are out there, but my perception is they are not getting any cheaper. I think the 3.0 upgrade announcement may have firmed up prices.