Why don't you hire a car with driver or taxi for the first few days, then, if you feel comfortable, rent a car.
You WILL NEED a driver's license. If the license you have has your name on it, even though it is in paper form (I don't know what it is because my licenses from the States and DR were always plastics) and says DRIVERS LICENSE you can keep your ground and claim those are the licenses they give you in England. Carry it with you, or at least a photocopy, when you drive, along with a copy of your passport. Leave the original in your hotel room!!
To rent a car you will also need a CREDIT CARD!!! Now, listen again, CREDIT CARD. It has to be VISA/MASTERCARD or AMEX. No DEBIT CARDS accepted. Even if it is a debit card with a VISA or MC logo, don't use it because the authorization hold will NOT get released and will be posted to your account as a charge and you will need to file a claim with your bank. The local card system (CARDNET and VISANET) are not able to issue refunds to debit cards or release authorization holds from debit cards! Only from CREDIT cards.
The car rental company will want you to present a credit card in your name and it has to have a sufficient limit to book funds on it. If you are bringing a prepaid voucher, count on about US$500 being blocked. If you rent locally with no voucher, AND buying complete insurance (CDW, extended CDW, and TP), count on about US$1000 being blocked, and finally, if you do not buy insurance but use your card's or other insurance, count on at least US$1500 being blocked on your card. This money gets released when you return the car, but you won't have access to it while you rent. Basically the "block" is equal to the deductible you get to pay for any damages (yes, there is at least US$500 deductible with full insurance, nice isn't it?)
Also, major car rental companies do not accept CASH deposits (Alamo, Budget, Dollar, Avis, Hertz, etc.) only CREDIT cards.
Some local rental companies may accept cash as a deposit, count on leaving about 1000 dollars cash if you are not local, AND your passport. Also note, that these local companies will hold you liable for all and every damage to the rented car, even if the car has full insurance.
This info is from a person (me) that deals in tourism and has a lot of experience dealing with car rental agencies (both major and local).