Regardless of house size, for two people, you only need a modest system. You could put a 40 tube/200L system in for in or around €4,500 which after the grant would be about €3500.
There was something wrong with the system you were using in the holiday home. I worry about solar panels on holiday homes unless there is a heat dump present. Very few houses have such a heat dump, but if the heat dump is set up incorrectly, it may have caused the problems you experienced. But in an unused house, the cylinder should be at 60 degrees no problem.
The system for your own house would depend on the number of occupants, and hot water use. Lots of questions, like do you use showers or baths? Is the house occupied during the day (needing more heat, but less storage than a house only occupied at night), is the roof roughly south facing? Is there a long run from the location of the panel to the cylinder? Do you have a preference for tubes or flatplate? Do you like to peel your potatoes in warm water????
Some houses use very little hot water - everything done in a dishwasher, occasional frugal showers etc., in which case there is lower hanging fruit than a solar water heater, but otherwise, it should stack.
During the winter, your central heating provides quite cheap hot water. Usually in summer time, the heating is off, and you are heating the cylinder, either with an immersion or by using the central heating system, heating a boiler, flue, pipes etc., just to heat a small cylinder. Both are very inefficient and push up the cost of summertime hot water.
Also, usually a solar installation incudes replacing your cylinder, usually with a more efficient one. That will give you some savings during the winter as well.
Lastly, isn't it just nice to have your hot water coming from the light, instead of some oil well?