Hi,
Yes they should have chain tensioners on the underside of the swinger.
Dragging clutch is kinda common I think on these bikes until the oil warms up a bit so I wouldnt worry too much about that unless it persists when the engine is nice and warm.
Plastics are a real pain to get especially the rear mudguards and seat. An 80cc item MAY fit but a bit of tinkering will no doubt be required.
The air filter had a black plastic housing that screwed to the sub frame I think?
Sorry not sure about oils and stuff?