From what I have read a square set of wheels reduces the tendency towards understeer, and some E89s came with a square set-up as standard.
I bought a set of 8J all round 17" Style 290 wheels from a 20i owner as summer wheels for my E90.
I must admit I was quite taken with it when it popped up on my A/T alert as I love Interlagos Blue and it has done 40K miles less than mine!
But I'm not sure about the interior, I prefer something like Champagne or Light Sepang.
And at that mileage it's heading towards needing replacement...
They should be fine.
I bought a set of 4 Kumho Ecstas for my Z4 in 2021 for just under £400 and haven't had any issues with them, although after 15K miles the rears were getting low on tread so I replaced them a couple of months ago ahead of a trip to Scotland!
That does seem unusual for an S54. Mine never needs topping up between oil changes that tend to be about 8K miles apart even though it has done 96K miles now and often gets driven as intended!
Maybe there is a slight leak somewhere? When mine had an Inspection Service on 77K the cam-chain...
Manual 3.0Si Roadsters are quite rare. It looks like only 695 came to the UK, and only 10 were Monaco Blue with Caramel leather, plus it's a low miler!