Convert a 7 speed to 8 speed on a 700 wheel?

Derailleurs don't have "speeds" they do whatever the shifter tells them to do. Your 7 speed derailleur will work with an 8 speed shifter of the same brand. Your wheel is another matter. If your wheel has a freewheel you will need to buy a wheel that can accept an 8 speed cassette. If your wheel has a 7 speed cassette, you will have to change the freewheel body, check rear dropout spacing, re dish the wheel, and possibly re space the dropouts to accommodate a wider hub. Start by finding out if your bike has a freewheel or a cassette to determine what parts you need to buy

I went from 7 to 8 in a mountain bike but I was already going to get a new wheel and shifers so it wasn't a big deal. If you have a freewheel cluster instead of a cassette, get a new wheel that has cassette, much better. The cassette will be narrower that a cluster and you may be able to put 8 on the spacing of old 7.

You can keep the same derailleur.

it depends

i did that with my road bike

nothing required

main thing is, is the hub and frame spacing matching>

derailleurs don;t have speeds

there are a dozen other things to check too though

since it is a recumbent it may have some oddball wheel and frame

wle