£7500 is too high for a 16 panel system. If you have the roof space for 16 panels it should be far cheaper than that.
I did look into mine for months before going for it. I ended up getting SolarEdge Inverter and optimizers. People with them all said they were hitting their monthly KW estimate or a bit more. Plus the warranty was really good. Small cost got 20 years warranty on all of it.
Panels, there are tons of brands. End of the day look for warranty, and performance life time. Most panels say they will still generate 80% after 25 years. Some like mine say 80% after 30 years. Thats written in the guarantee of the panel.
I did go overkill and got about 8 quotes. My fave was from a company called TP Solar. But they are nearly 140 miles from where I live. They would come out for any repair, however a local company 4 miles down the road came in only £8 higher on their quote so thought local were best.
On the subject of quotes, my first quote was nearly £8400. for 14x 250watt panels. After shopping about and researching I ended up paying £6317 for 14x 285 watt panels.
Worth haggling.
Look at solarguide.co.uk plug in your post code, system size, roof direction and that will give you a rough idea of how well your system will really do.