Is it best to load minutes on a new Orange cell phone or sign for a plan?

If you are going to be living here, I think a plan is the best way to go. If you have to start with cards until you get an address, you can switch to a plan at that time. Take your passport with you when you go to buy your phone and sign up for service.

They have special pricing for people who buy phones at same time they sign up for service.

I don't think address is a problem. They never send out invoices anyhow.
So just give them your hotel's address/

You can sign up for Flex plans hassle free. Just a passport and money.

Max plans (open plans) will not be available to you, as you would need a dominican bank account or dominican credit card as a credit reference.

Flex is a good choice. That is what I have. The price will depend on how many minutes you decide on per month. It starts with 60, 90, ........ The minutes are cumulative, what you don't use one month roll over to the next month,

Flex is a good choice. I started with Flex, now I have Max. Flex is only a tiny bit more expensive than Max. After you run out of your Flex minutes you purchase prepaid cards, but the minutes are still charged at cheap Flex rates. So there is no penalty for going over the minutes, like in the USA where they hit you with 40c/minute. Here, the more you call, the cheaper it gets. Also, after you run out of minutes, you will be able to call other Orange customers on weekends for just 1 peso per minute (only available to Flex and Max accounts, pay-as-you go do not qualify).

You can do the same thing with Claro, and their Control plan, and have the same 1 pesos rate for Claro and Codetel numbers.

Orange Flex

How does the Flex plan work as far as payment? Is it paid monthly. Can you have it billed to a credit card with an american bank?

You used to be able to use foreign credit cards but now you can't . You have to pay cash each month. You get your minutes on 16th and pay by 25th. I used to be with Orange Flex contract (for 5 years) but changed to Verizon as I was fed up with lack of service, coverage and the fact they stopped taking the money automatically by credit card from UK.