Hi JC -
You need to be comfortable with every step of the process. The Realtor and mortgage lender should be working together to get you the best package for your situation. You have every right to be detail oriented - it is probably the biggest purchase of your life! The reason the lender does a 30 day approval is because the credit report is only good for that length of time. As long as nothing has changed with your credit, you should be fine. Once you find a property and have a purchase agreement in place, the lender will pull your credit again to submit to the underwriter. They don't want to keep pulling it every 30 days because too many inquiries can bring down your credit score.
As far as the closing cost assistance, FHA allows up to 6%. Your Realtor should confirm this amount with the lender. Every property is different (i.e. value, equity, seller's position) so it could depend on the home but in general, 6% is allowed. Hope that helps. Good luck to you!