Im glad I didn't get a Cupra. An FR is definately cheaper to run / insure / buy in the first place as you say. MPG on mine is very impressive, I got an average of 54 on a clear Manchester - London run recently. It's still running fine overall & I remain very happy with it.
You've just got to find a trim level that ticks your boxes. Heated leather seats, 18" wheels, adaptive suspension & the digital instrument display are a hard combo to find for some reason.
Shop about, I had to travel quite far to get mine. But it was the only one like it listed anywhere at the time.
Boot space is fine for a bike. I do a lot of cycling and I get a road bike in the boot with just the front wheel off. This is with the rear seats still up. I don't think a mountain bike would do that though, a bit of a longer thing overall? The carrying capacity is just good full stop. Been on holiday a few times in the UK with enough stuff to keep my 1yr old going. It's a solid and sensible choice, you wont regret it.