i fixed 1 last year that was as bad,if not a little worse than that.wasted 7 weeks doing it,you will never make that pretty and if you do it would take forever.
best thing is reshell or sell all the parts and buy a good 1,yeah,it has an rs turbo logbook and chassis number,but how many folk who have said save it would be willing to pay the same as what a good 1 costs if you were to sell it when its finished,nobody would and it will cost far more.
as for making a s1 rep,it will be easier and cheaper buying 1 and it will last longer too.save yourself the heartache and weigh it in,im talking from experience as i got mine mot'd then broke it!
i welded nearly every panel on it,even the roof needed welding,i scrapped it after doing 300 miles as the turbo went,it needed an alarm and id spent enough and was sixk of it.
its your car,do what you like but at the end of the day id rather have the best shell in the shortest amount of time over a bit of paper which says rs on it!