You responded with one liners and never explained. If UK regs don't apply to you it is up to you to say so. You were given the reasons why a DIYer can't install an unvented cylinder in the UK and a better alternative. That is not preaching.
The DPS sites give a load of on-line, and downloadable, design software. What you need is calculate the rad sizes, then this will give you the boiler size. Calulate the heat bank/thermal store size with the appropriate software on the DPS site. Then you can get a heat bank that has all the controls, motorised valves, elecrical box, etc in one package. Look at the DPS site for customers examples. All you need do is connect up the boilers flow and return and the radiator flow and return to the appropriate connections, the power, clock and the room stat. These can be pre-wired into the box and it is a matter of running a wire out to each component.
Then it is a matter of sizing up the CH pipes.
Firstly get kit which can be serviced with available parts where you are, and that locals can service. What is the most common oil boiler with parts available on the islands? Get one of these. Heat banks are simple and service free. The locals probably will not have heard of them, but the logic is easy to follow for even a dumb plumber. Unvented cylinders require pressure controls and if these go then you have no hot water and you need to source the parts and no hot water.
Try DPS as a first stop, I'm sure they have a design service. They may throw that in for free if you buy a simple heat bank from them. They will need a plan of your house. This probably can be on A4 paper, with room sizes, what type of walls and floors, windows sizes, single or double glazed, insulation levels, boiler location, heat bank location, etc.
A TIP: Go for an "integrated" heat bank, which provides CH and DHW, with a large backup electric immersion. If the oil boiler is down then electricity will heat the heat bank cylinder, and hence the house and hot water until the boiler is up. Essential in a part of the world where most parts have to be imported and may take time with long outage times.
Integrated heat banks are the only devices that give full CH/DHW backup.
Heat bank use standard heating pumps. I assume these are available on the islands off-the-shelf. They operate on flow switches, which probably are not available on the islands, so it may be worth your while ordering one of these as a spare, just in case.
Is all equipment British? Don't you import any from Argentina? If so are they local makes or imported Italian or Spanish?