That stuff in the boot is the least of those worries, looks like a fairly solid one tbh from the pics although not a patch on mine

Front wings are not too much of a problem, they are available, easily changed and commonly rot there.... I would want to look a little deeper into the bottom of the front n/s wing where that is rusting as this can be more than superficial and front floor area can rot badly. The main other thing to check is the rear axle carrier area, that is a common killer ! There a probably better ones about for little money unless this is a giveaway and you have time on your hands.
The sport seats are exactly the same as E30 ones in construction, can't speak for the comforts though...
Mark.