We've been parking our Teslas in the driveway (garage too full and not tackled yet) and charge outside on the driveway so no problem not having a garage. You can preheat or cool your car with your app before you get in it to go so comfortable regardless of the season.
Since you already are an EV family (at least with your wife's car) that's great. No need to sell you on the benefit. Teslas do offer more in the way of pleasure driving and fun in general IMO than any other EV out there. You didn't say if the kids will inherit her Prius but if they do or if they might be at home for a while and also want to drive an EV like a Leaf, then I'm going to suggest installing a NEMA-14-50 outside. Doesn't have to be in a garage, doesn't have to be mounted to your house. I've seen people sometimes run an electrical connnection to a short post that can be more easily moved at a future date. Just need a weather proof cover. The NEMA 14-50 would give your family more versatility to charge (and anyone coming to your house as a guest that needs a charge). I take advantage of the 11pm-6am low electricty rate on my LR AWD Model 3 (310 miles) and can fully charge overnight during that timeframe. Of course the HPWC is great and is weather proof too and is an all in one solution for charging but you will be limited to only Teslas being able to charge with it. So something to think about. When you get your garage built you can always install one there and have the NEMA 14-50 also available.
BTW a NEMA 14-50 outlet is VERY desirable with contractors working outside and needing a supply for their power tools. Before we got our garage outlet, the guys working on redoing our backyard (bbq island, pergola and installing stone pavers) were using our outdoor outlets which couldn't handle all of their power tools especially if one guy ran a saw and someone else wanted to use another piece of equipment. I was always resetting the GFI to the outdoor circuit when the power would invariably go out. One last point or two for use of a NEMA 14-50, it's RVs friend and I understand hot tubs would require them too.
If your wife is open to buying a Model 3 for her use, I'd say go for it. I absolutely love driving mine
every day (not exaggerating) and so glad we didn't buy another brand when it was time to retire my car (btw it was a 2001 fully loaded Toyota Avalon which I got many years of service out of--but would never say I Loved driving it like I do with my Model 3). Cars are expensive and you get yourself tied to owning one for a while before you can buy another. So you really need to choose wisely especially with so much going on with the future of EVs in flux. Tesla has designed their cars with so much forethought and with the updates, I just feel you won't be making a bad move on a car that will age with you. If you can swing it, let her enjoy a Model 3 now. It has a great safety record in crashes too.
Oh and the Boxster owner might find he enjoys driving the Model 3 as well
. What version are you guys thinking about? I don't have the performance version but find the AWD version with the LR battery fast and fun enough for my use.