110/220v - same as in the US
Merchant fees here in Mexico are outrageous. Therefore, it is very expensive for businesses to accept them...and is why you will find that many small businesses simply don't accept them period. Jim said that some will charge you 10% to use your credit card...this is not completely accurate. Our sales tax is 10%, and has to be paid whether we take cash or credit card. However, some establishments will offer a cash discount. If you pay with credit card, this cash discount simply goes away, so it is costing you 10% more to use your credit card...but they are not actually charging you 10% more, or shouldn't be anyway. It is customary for a 4% to 6% additioanl charge to apply for credit card taransactions however. Merchants here are charged this PLUS sales tax on top of the fee...so it really takes an unreasonable chunk away from the merchant and into the hands of the banks.
Here are my "money tips" for Cozumel:
http://www.bluextseadiving.com/moneymatters.php
Yes. The average base is $5 per tank per diver, so for a 2-tank dive, $10 for you and $10 for your wife. The crew typically pools the tips.
Restaurants, 15% to 20%, as is customary in the states.
Be very careful about this. If they are very friendly, informative, helping you with luggage, groceries, giving you an island tour, etc. then yes. If they are driving you from point A to point B like a bat out of hell with a surly attitude, then I would say no. Also make sure that you have small bills or monedas (mexican coins) because one of the biggest tricks many of them pull to earn more tips is to play the no change game...even if your fare is $4 and you give them $5...they'll say, "sorry, I don't have change." If they do this, then tell them to come back to you when they do...this is unnacceptable and is grounds for automatic no tip in my book! I bet change will magically appear!
There are some very nice, freindly, outgoing, helpful taxi drivers...but there are just as many looking for an oportunity to cheat you. So just use your judgment...and if they have a bad attitude, well...it's your money, so do what you feel is appropriate.
Yes there are sidewalks and walking around Cozumel is very safe. Just use the same basic precautions you would use anywhere...be aware of your surroundings, don't walk around with money hanging out, etc. and no one will bother you. DOn't make yourself vulnerable in otherwords.
My two personal favorites are Le Chef and Especias...although there are many great restaurants here
(Sonora Grill, Mission on 30th, El Moro, Camilos, Casa Denis, Guidos, La Cocay, etc.)
Here is my restaruant list:
http://www.bluextseadiving.com/restaurants.php
Where will you be staying? The AI hotels have many of these activities available on premises complimentary or for a nominal fee.
Ice machines are FINE! NO ONE, I repeat NO ONE is going to serve you tap water or ice made with tap water...the locals don't even drink it. ALl ice is purified as is water that you will be served. Some of the larger hotels do have water purification systems, so they will tell you (or there will be signs in your room) that the water is potable or not. If it says not potable, then don't drink it.