It's probably not a good idea to get too personal when providing this information, and especially stay away from comments like "I've loved writing ever since grade school" or "My sister, mom, husband, etc. think I'm a fantastic writer." This is a huge turn off. You can say things like "I'm married and live in Anytown, USA, and work full time as an aerospace engineer." That's plenty on the personal end. By no means should you never send along a 250 word bio unless specifically asked for one. A little about yourself means just that. What you choose to say reveals a lot about what you might be like to work with. Do you follow directions? Do you tell a little? Or say too much? Very important.
As far as credentials, you do belong to an active writers' community, yes? AW is fairly well-known. Are there other groups you belong to? Do you have a critique group? This would indicate you're serious about your writing.
As competitive as this industry is, agents are looking for an excuse to send a rejection. Don't give them one if you can help it. They really do look at credentials and credits, and if they're trying to decide between two queries they like and one author belongs to a pro group and the other doesn't, the one without the affiliation could be the one left behind.