Original size is 165R15, equivalent size is 165/80R15.
No.
between the rear wheels
1974 was the first year of energy absorbing Beetle bumpers. You can't use earlier bumpers on 1974s.
Yes, since that's a tautology. Unless you mean "would additional seats fit in a vehicle without taking the original seats out first", in which case it would be a pretty tight fit, but you might be able to get them in the back. There isn't much room in the "trunk" (which in a '74 beetle is actually in the front), and I doubt you could get them in there.
correct it will fit. be sure to take lots of pictures before you pull all of the wires off. so you have a diagram of where they go after.
No, a 1967 Beetle hood will not fit a 1974 Beetle without modifications. The body design and mounting points of the two models differ, particularly due to changes in the front end and the shape of the hood over the years. If you want to swap hoods, it would require adjustments to ensure proper fitment.
I doubt very much they will fit as the bolt pattern would be different.
The 1975 regular Beetle windshield will fit the 1971 Super Beetle.
bolt pattern is a broad term, so I'll assume you're talking about wheels, in that case 4x130mm
a 912 Porsche engine will fit in a beetle
Not without a huge amount of work. Until 1968 VW used swing arm rear suspension. In 1969 they changed to Independent Rear Suspension, with CV joints.
NO! 17 wheels do NOT fit a corsa