Onething is sure, that they dont accept cash. Only DD or Cheque. (second investment onwards you can use ECS if available).
They require PAN for any additional investment. ( I am not 100% sure, ask your scheme's toll free numbers or emails.)
If you want to redeem money from MF, (no matter how much it is) they will give you a DD or cheque, or they can directly credit your bank account. It doesnt matter whether you have a PAN number or not, or whether the money is less than or more than 50K.
Soon they might freeze the folio number if you dont submit PAN. I dont think such an order is enforced already. But they might do it pretty soon. (They did that to demat accounts, ie freezing demat accounts that doesnt have a PAN. Now around 8 lack demat accounts are frozen. Some 50,000 for them have some stocks in them).