There are many fees, taxes, expenses and costs that will be attributable to the condo you finally choose.
The annual cost of the mortgage is a function of the purchase price, and then of course how much you finance--and the rate you get for the mortgage. If you are paying cash, then in reality this is zero, but as an investor will tell you, there is a cost of using your own money--that is however, for another discussion.
There are insurance costs, which you will want to be sure of. In Florida we have two insurance policies, one covers liability and includes fire and theft (and covers the furniture in the condo as well as contents of your car), the other is called wind. Wind is basically hurricane insurance, and it's expensive. I use an insurance broker in Englewood (one town south of Venice) who has done a good job finding an attractive set of policies for me. Depending on the condo you pick, you may or may not be responsible for the wind policy, and you may be able to just carry a "tenants home" policy.
Condo fees are charged monthly--whether you are there or not. Usually these cover exterior maintenance, lawn mowing, pool cleaning, common area cleaning, driveways and entry gardens, lighting--and maybe more. Each condo association will have a set of "documents" which will tell you what is and is not covered. The Realtor will give you a set of these "DOCS", you should read them.
What if there is a unique need at the condo--say the board of directors decides to reroof the units or repave the driveways around the units, or the pool collapses and they are faced with a large repair? You will get a bill for this special assessment, and it may be in the thousands of dollars. Not uncommon, so ask if the condo has a cash reserve for emergency use.
Taxes are charged by the municipality and if you have a mortgage, usually the bank will offer to collect a monthly amount from you and then be responsible to pay the taxes when the annual or semi-annual bills come. When you find a condo to buy, the prior year's taxes are known--but in Florida, if the seller has "homesteaded" the condo, the taxes may be unrealistically low, and will certainly escalate on the transfer of the ownership, maybe many times over. Review other units in the complex to see their taxes.
Of course there are the utility costs. Electric and water and telephone and cable TV and possibly gas as well. These are usually based on a monthly connection charge, plus use. So you will get a minimum charge when you are not in residence (when you are in the UK, the bills will continue to arrive for electric, and water) and when you are in residence, the meters will be running on the additional use. But you can't shut off the electric here for fear of loss of air conditioning which leads to dampness, bugs and mold.
And then general maintenance costs. Things in Florida wear out faster than elsewhere. If you are leaving something outside--say a gas grill--it will rust/the hoses will deteriorate/it will break. Batteries in cars quit before their time, lawn furniture simply wears out. Plumbing corrodes the copper pipes from the inside due to acidic water, so expect to get friendly with a repair service.
Still, it's a great place to be--I live here. But you might want a Realtor/Property Manager to keep track of all the above and make it a little easier if your plans are to be here for only a few months at a time. Usually the property manager will also find a tenant for you and collect any rent that's due, plus arrange to pay these expenses and monitor the unit and it's condition on a weekly basis. Here's a little commercial, if you want that service, I can arrange it for you. Best regards.