1) Do you have a contract or service agreement signed by each of your
clients?
I use a letter of agreement which is sent via email. When a new client pays their deposit it signifies their agreement with the terms set forth.
2) Did you have an attorney look over your contract on did you just use a
template without seeking any legal advice?
No, I didn't use an attorney and I didn't use a template - although that's definitely not the norm and I would recommend at least having a legal eye look over any paperwork you intend to use as framing a commitment between you and a client. My clients are all on referral (ie - they're all friends and or colleagues and business associates of eachother) - since we don't accept clients outside that circle I haven't had need for something quite as heavy as a contract.
3) Is there any specific item you felt was missing from your contract?
Initially I did not include a late payment policy - this became necessary after we'd been in business about a year. We're quite friendly with all of our clients and while this is great for business also can lead to some relaxation in the invoice due date department even on net 14

Once we instituted late payment penalties it became a non-issue.
Hope that helps!