My advice is to go to the SEAT UK website, and play with the finance pages, sometimes an offer for £250-500 extra off pops up, this is a SEAT offer, not the dealer, so print it and put it in your pocket. Only get it out when a deal with dealer is agreed (unless they have already told you about it and asked for the code). I think there is interest free at moment (subject to a minimum deposit)
I would save the money on paint protection (at least at dealer rates of £350ish) and buy the 5 year factory warranty (can't be added after it is registered), the later add on warranty has many exclusions compared to factory one.
If you want paint protection get it done elsewhere for less than half the price. Similarly things like gap insurance are much cheaper bought separately
If they can find you a stock vehicle should be about 2-3 weeks (as held at UK port), bit longer if in transit. If they offer you a factory build expect 8-10 weeks + 4 weeks delivery (say 3 months) plus time for factory to accept order (which can be many weeks, especially if dealer has already used up their quota). Each dealer only gets a quota to spread the allocation between all European dealers (but wont tell you if they still have quota this month unless you ask directly)
Always worth asking if there are extras that they will add for free, could try for a spare wheel, or armrest, or boot liner etc (if not already included). Work on the basis if don't ask, won't get, if get nothing, then no worse off having asked, but might get bonus item.