Car appreciation... the aesthetics, the engineering, etc

i have decided i love my cheap 1.9 td 406 after an adventure in europe. there are some issues though.
we got a engine warning light 1700km from home, decided the fuel filter housing was leaking having wrestled with this before, by passed whole filter unit and installed cheap inline filter, and had no problems since but now need to decide what to do. i do want to get rid of the peugeot piece of crap, i would like to get away with see-through plastic or glass inline filters but i would like to know which ones are better than others and how ideally they should sit in-line and in relation to the pump. i also need to know how to deal with the wires (sensors?) and the heating/coolant circuit that goes through the bottom of the filter unit i plan to rip out. lastly, i’d like some sort of heat exchange or electrical thermostat unit but am not sure what solution would be most elegant and cheap.
there are also some other issues: i need to do something about the sunroof that ideally doesn’t rely on electrics or existing waterproofing as both are shite.
I want new non-electric front seats but am unsure what is good and what will fit.
I need to do something about waterproofing and soundproofing elsewhere in the car.
i want to fit the led fog lights i got on ebay but am not confident these will be plug and play.
currently my best hope(s) is to do some of this myself, meet an aspiring mechanic who will want to work on these things with me to get experience, make a new friend, or work out which bits really require a garage and which bits don’t.
When people say they ‘went to the local scrap yard and picked up…’ what actually does this involve doing and is it possible in the middle of london?