1 - Nobody has ever asked if I have a GitHub or StackOverflow account. This might be different for high-priced jobs, but for everything I've done it's never come up. Normally a quick email exchange or phone call has been enough.
2 - I found my first client on oDesk, and they referred me to just about everyone else. I haven't used it since, and it's thoroughly depressing to look at how low pay the jobs are. Posting in the HN freelancer topic, and posting an ad on /r/forhire is another good way to get clients.
3 - Whatever you want - there are tonnes of people that need software building (and plenty that don't even realise it). Just remember that a few hours of time can quickly get eaten by emails, phone calls, "can you just check this", bathroom breaks, leg stretching, quick drinks etc. It takes a while to get in a good rhythm.
2 - I found my first client on oDesk, and they referred me to just about everyone else. I haven't used it since, and it's thoroughly depressing to look at how low pay the jobs are. Posting in the HN freelancer topic, and posting an ad on /r/forhire is another good way to get clients.
3 - Whatever you want - there are tonnes of people that need software building (and plenty that don't even realise it). Just remember that a few hours of time can quickly get eaten by emails, phone calls, "can you just check this", bathroom breaks, leg stretching, quick drinks etc. It takes a while to get in a good rhythm.