Even the perfect car might have the odd issue fron time to time. Even Clarkson described it as (probably) the best car ever made!!
Mine is also a '95 MkIII.
At 6'2 I have never had an issue with the seat; tip the long adjuster front and back until the swab is virtually on the floor.
Please be a little more desciptive re C/C and front demist. C/C will set the a/c if you hit (I'm using modern terms )auto. Revs will increase. The f/s demist will overide the auto and the blower will direct everything to screen. The orange light will come on. Does some or all of this happen?
Notwithstanding other suggestions, the flapping noise may be due to engine cover or wheel arch liners, something trapped between the grill and condenser (front radiator to some folks), something trapped in the air intake or previous owner clinging on for dear life .
Heated seat needs new element. Most dont bother because of the difficulty of fitting and warms it up in moments due to quality of upholstery.
Side light issue; in some years of ownership and membership on here, this is the 1st time I've knowingly come across such an issue. They are not easy to get to so I would suggest aquisition of a replacement from Benfur ( use the pm facility, he's a trusted member). In the meantime drill a small hole for drainage.