You'll definitely want to run some usage numbers, what is your daily usage of electric roughly?
DNO fee seems a little steep but not sure how much work it is to apply, in my case the network operator replied to confirm that the fee to add my G99 was £0!
Can't say how well Sunsynk compares to Givenergy, I have the latter and it's really good, and gets active development, so it can tie into smart tech like TOU tariffs with Octopus, and Solcast forecasting.
If you ever intend to add an EV make sure it's a Hybrid inverter you are adding, so it can handle adding a charge point to the system.