Ouch. You don't lose custody or parental rights just by moving out. Some times that is actually in the best interests of your children. You can lose your sanity, lose some points on your credit score after the bills start piling up because it is more expensive for you two to live apart, lose some personal belongings.
With a net pay of $450 and wanting to support her I recommend ditching the attorney idea. WHen I got divorced it was not amiable, I was makign $10 / hr fighting for rights to see my kids and paying $150 / hr to an attorney. Now you can't find a decent one that inexpensive. Keep your money. If the two of you are agreeing on everything then find out how to handle the divorce without attornies.
Come up with a reasonable parenting plan that works for your kids. I will never regret my decision to stay in my kids' lives. It was tough (since, unlike you, we didn't agree on that part). If you want to be a dad to your kids then no one can stop you. Do what you can, lead by example, forgive or let go of the rest. You may find that in the lond run you haven't lost anything.