Soldato
See this is what bothers me they are already ripping you off with the panel costs and that is the first item on your list. The Eurener 410w all-blacks panels are only £148 (ex VAT) each, so 8 would cost £1184, and that is at retail pricing not trade, and the inverter is only £950 (ex VAT). Ye they still want to charge you nearly £3k for the install work, as well as making huge margins on the parts.Equipment Costs
8x Eurener 415W all black MEPV108 solar PV panels £1,801.87
Regarding only fitting 8 panels, are you restricted by height and width, or just one of them? You could perhaps fit larger higher wattage panels if you have some give in one of the dimensions, as those panels tends to be 2-2.2m x 1.1-1.3m instead of 1.6-1.75m x 1.1m. You'd be looking at 500w+ panels up to 670w depending on availably and the use of a compatible inverter.