My best advice is to search your state's website for your responsibilities. Most states have some sort of guideline for landlords.
1. Either will work. Never thought of a P.O. box but it is a good idea since I have tenants surprise me at my house to drop off a check with no notice.
2. In CT we must provide the tenant a Security Accounting Statement with in 30 days with the whole or partial deposit including interest. Explaining any charges. If not they can sue for double the deposit.
3. The utilities will control how you handle it. Here they just transfer them to my LLC with a phone call. If the tenant moves and a new one moves in within a billing cycle they transfer directly. We just make sure the tenant leaving is current before returning the deposit.
4. You are the Managing Members of the LLC. I do introduce myself as the landlord but I use the title on all correspondence to make sure that I treated as a business corporation.
5. If they don't qualify they don't qualify. You don't have to rent out to just anyone. We do credit and background checks on everyone.
6. we charge a late fee if paying past the 10th of the month. We bill them direct as a incentive to pay on time. If you have to after the fees that is one of the things to include in the Security accounting Statement.
Most important is to make sure you are compliant to your states regulations. I have made many mistakes out of ignorance luckily none have come back to bite me.
Best of luck