The Extreme Update applies to the Home Patrol 1 and 2 scanners only, it adds a few features for advanced scanner users like trunking analysis and advanced searches.
The BCD436 and BCD536HP have a ProVoice update that adds ProVoice digital to these scanners, if your area uses ProVoice then this is a good option for you.
The Setup and Optimize service includes updating the database and firmware of the HP1, HP2, 436 and 536 scanners, setting up a Favorites List for your area as well as setting the scanner location for you. This costs $39.95. You could certainly do these things yourself for free, the radios all come with the cable and software to do it as long as you have access to a Windows computer. If you don't have a computer or just don't want to bother with it then it might be worth it.
As for Phase 2 digital, the BCD436HP (handheld), BCD536HP (desk/mobile) and the HomePatrol 2 all handle this. The HP1 handles Phase 1 only.
For the antenna, I usually suggest that you try it out first with the included antenna and see how that works. Outside antennas can be expensive and difficult to install. Replacement local antennas may work a little better than the stock antenna.
As far as how good a dealer they are I cannot give an unbiased opinion on ScannerMaster as I work there but if you have additional questions feel free to call us during the week. Even if you do not buy from us we can usually answer a few questions for you.