Congrats! I think you'll enjoy it just as much as your WRX. I've owned 3 STi's prior to owning Teslas and there are definitely a few things I miss as others mentioned (stick shift, engine/exhaust noise, handling). However, the other items out-weigh it so I can't really ever go back. I still find myself searching for used STI's pices from time to time, but then remember the maintenance along with other costs associated with owning them.
One thing I love is that I can just romp on the car anytime, no more baby-ing it until it's warmed up. No more thoughts around, "I guess I shouldn't push it too mujch since I've been pushing it a lot lately..." etc.
As a fellow former STI owner, I'm with you 100% on all of this! Though I feel it's best to let the Tesla drive unit oil warm up a bit if the car has been sitting overnight before really getting the hammer down, but it's not something I've ever seen Tesla suggest, just something that makes sense to me. Maybe preconditioning warms up the drive unit oil too, I haven't checked for that. (I assume oil temp or at least some drive unit temp sensor is available from the debug / data logging access, I'll get something setup for that on my M3P soon.)
As a long term Model S owner I can say you're 100% right with this concern as well. Though these days you can buy parts from Tesla, and also Tesla's repair labor rates actually seem on the reasonable side compared to traditional car dealer service rates in my area, especially if comparing like-priced ICE brands (i.e. "luxury" brands).I do however worry about long term ownership of a Tesla, which is why I've never owned one a long time. Being that you can't just buy any part from Tesla, and some of the repair costs prices I've seen on older Model S's (makes my STi repairs feel like pocket change), I don't know if I would ever keep it long term. But that's just me since I usually did all the repair/maintenance on my STi's myself.
The parts catalog is online at Parts Catalog and you can order them through any service center. Unfortunately they don't have a dedicated parts ordering system or parts department staff, so you have to place the order and get communications via a service request, which is clunky, and selling parts is generally a low priority for overworked Service Advisors' time. On the flip side many people have reported Tesla voluntarily dropping off their parts via mobile service staff for no extra cost / no shipping cost. (On my only experience ordering catalog parts so far, I picked them up from my local SC, they never mentioned and I never asked about having mobile service deliver them.)