As others have said, that looks like a good buy and price doesn't sound unreasonable either given the huge jump they've made in recent years. I've had various 205 GTi's over the years and still have three (two 1.9's and an Mi16), all bought when they were worth buttons compared to now.
In terms of the leaks:
That hole above the boot lock normally has a plastic peg from the slatted tailgate trim going through it with a securing star clip - they get broken when people try to remove the slatted panel not realising that the clip there, and the hole that's left will let in a little water, which pools inside the tailgate before running out the vent holes in either corner. Check the other various holes on the tailgate and the glass bonding, as all can leak to varying degrees.
That said, unless it's leaking very badly and the car has been parked on a fairly steep downhill slope, I suspect that's not why the footwells are wet. Rear footwells are usually the rear quarter window seals leaking as they shrink with age - new ones are available - or sometimes because the sill drains are blocked and it leaks in through the seatbelt mounting holes. Front footwell could be water travelling from the rear, but the amount that's there looks like it's leaking from the front - front screen seal, scuttle panel, A pillar seam, door seals or the plastic scuttle plastic trim not being fitted properly are all common causes.
If there's that much water pooled on the carpets, then I'd strongly suggest taking it out as the felt underlay will be completely soaked and won't dry out, making the car mist up easily and eventually rusting out the floorpan.