Hi - There's a good few years life left in SD and a wise choice would be for 2 matching cameras with really good lenses and some high quality mics.
Many will say it's far better to have well filmed weddings on SD than poorly shot weddings on HD. Same with tape, there's lots of video companies shooting on tape, as we do, though we use hard drives on the cams as back up, and for speedy downloading, as well.
At the end of the day it's your choice, but if you're undecided about the venture it's a far cheaper option to go for SD to see if you can produce the goods that will be in demand rather than shelling out many thousands and find you're not suited or don't have the eye for it.
If your partner is the friendly type and can coax the undecided into buying into your services, then yes, let him meet the clients. One day, providing you produce high quality weding/event videos, you'll have enough work and recommendations to invest in higher quality kit and target higher quality clients too.
Hope this helps!