Thank you Simon this is very good information!
Happy to help!
I defer to Simon who works at PG Music. I would only comment that BIAB now appears to have a higher reliance on processor power than it did a few years ago, because of the greatly improved speed of handling the RealTracks.
16 GB of RAM will work but 32 would be helpful if you have anything else running. External storage is less expensive now so I would save on that in favor of 1) the better processor and then 2) 32 GB RAM.
Provided internal storage can be replaced, yes. If storage is soldered to the motherboard, buy as much as you can afford. Flash storage wears out with repeated writes, and the more you have the longer it will take to wear out as writes are distributed across the available space. If storage can't be replaced, the laptop goes in the bin - though that goes for any other part too...
If RAM is soldered to the motherboard, then I'd also buy as much as you can as doing so prevents you from having to upgrade quite so soon. Thankfully popular business machines tend to be upgradable - the Thinkpad T series for the most part.
the reason being...internal components and mother boards and other aspects can change sometimes. also your studio needs might be vastly different than another person eg track and plug in counts and other variables.
soooo...your best bet is to get a 30 day return guarantee and run the tests itemised in the link below. notice most importantly the dpc and other tests.
purchaseing a pc often is a crapshoot hence the need for tests.
Which is part of the reason to buy business class machines.