#3 provides the main clue to a solution. If you want to get email every time someone calls on your POTS line, then the
SPA-3000 is the way to go. You may or may not want a two-line cordless phone once you get Asterisk handling everything. We use the 6688 from Uniden (2 lines) with Asterisk to handle two different extensions. This lets two people talk at the same time (one BV and one POTS). You can set it up where one extension answers your POTS calls and the other one handles BV. Works great. Take a look at some of the
SPA-3000 setup suggestions on Nerd Vittles to avoid a lot of frustration.