I believe there is a small annual custodial fee for accounts under $10K. It used to be $20 per year. It goes away once the account hits $10K, so you'd maybe pay it for a year or two at most.
If you're opening the newer Vanguard brokerage-style accounts, buying the fund may be a two step process: You deposit your contribution in cash. Once the deposit arrives (a day or three later), you log into your account and make the purchase transaction.
I've got things set up so I've linked my checking account with Vanguard. When I make contributions, it is all one process - I just say I want to contribute $X to my IRA and to buy fund Y with it.
I won't give you advice on what fund to put it in since there isn't enough information about you to give advice, plus it's my policy not to give advice. You should consider the funds' asset allocations, costs, investing style (active or passive), and to what degree you want to invest in foreign investments. You should also consider your other assets and resources (the inherited RMD, child support), risk tolerance, and plans and goals (college for those kids?).
Good luck.