It's been awhile since we used these (we are getting ready to switch back to them in prep for potty training) but I don't recall changing any more diapers than I was when I was using regular disposable diapers. If you are leaving the house at all, though, you may want to consider adding a third type of disposable diaper to the mix. gDiapers come with a little wand that you swish in the toilet to break up the pieces before flushing. Unless that process has changed, I'm guessing you don't want to 1. have to carry around that wand and 2. stick that wand into public toilets.
I really liked gDiapers. For our son, when we did use them, they worked great. How often you wash the outer cover really depends on whether or not the poo leaks through the inside cover. If your baby's poop is generally pretty runny, this might not be the diaper for you as the consistency would be hard for the gDiaper to contain. But if the poo is regular old poo, you'll probably really like them. If you compost, the wet diapers can be thrown in there so that is an added bonus since you are trying to be more environmentally-friendly.
The Velcro did not seem to deteriorate from the washings. The instructions recommend closing the Velcro tabs before washing and I think this helps if you can remember to do it.
As for your last question, I can remember my mom sitting near the toilet dunking our diapers in there to get off any gross parts before placing them in the washing machine. She would then use hot water and bleach. (Do people still use bleach?) Anyway, pee diapers, of course, are a no-brainer, just wash 'em as you would any other load. But with the poo diapers, you want to remove as much poo as you can before placing them into the machine. If you think there is any weird residue (for lack of a better word) left at the end of a load, you can also run the rinse cycle again or something to ensure your next load of clothes doesn't get tainted.
Good luck!
(I did a few posts about the gDiapers on our blog. You can read them if you're interested: http://darrenandchristie.blogspot.com/search?q=gdiapers)