I've mapped a similar trip from LA to Vegas on ABRP app several times, both with and without Tesla Supercharger access. Two stops both ways factoring in at least 20% SOC on arrival in Vegas and Home.
SR XLT made the most sense for me. Given your daily commute you'll really love the truck. I am a huge proponent for at-home level 2 charging. It really enhances the owner's experience IMO.
Yes you are correct. The ER comes with the extra charger. In this use case, I don't believe he is opting for the ER battery based on the MSRP target specified.
I recently had my FCSP installed. You do not really need it for the MSRP price. If you can get it for $600 I would, otherwise, I would consider getting the new Tesla charger when it comes out. Because you're getting an XLT you do not need or can use the full 80A that the FCSP can provide.