Can I use diagnostic tools on my own car effectively?

The thing about these gadgets is that while they may tell you what the recorded fault is they don't tell you how to fix it.

I'd just mention that it'd be an idea to rummage under the seat. There's wiring down there which tells the car if the seat is occupied, and if that's loose or faulty it can give rise to spurious airbag and seatbelt warnings.

Being an ugly american I am accustomed to seeing $$$$. ££££ threw me off, I lol'd.

Over here many parts stores will hook your vehicle up to a scanner for free and then tell you what trouble codes it is throwing. I'd check into that, I bet they have the same service at part stores in your area.