Welcome to the forum!
Lots of knowledgeable people on here, so I am sure you'll get some info that's useful.
My general advice to new players is to not spend too much money now, wait, do 4-5 games. There are bits of airsoft that are awesome, some bits that are a bit.....meh. Some people can handle the meh bits while others can't. Lots of people start airsoft, only a few carry it on for years, so hold back on your spending as much as you can for the moment. If you're still loving it in 4 games time, then yeah, spend and buy good stuff. It'll also give you an idea of what you'd like and you'll see what other players use, start with and then quickly get rid off.
I'll also challenge your view on having real firearms, you can get firearms in the UK, you need to have a reason (such as a member of a shooting club) and jump through a few hoops (letter from a doctor, people who will be a reference, criminal background check and a chat with a copper) but it's all very doable. UKPSA and Practical mini rifle/shotgun/pistol are becoming bigger in the sport with lots of opportunity for fun, in addition, longer ranges/bigger calibres are available in restricted formats, but there are a lot of interesting options.
I love seeing father and son combos on game days, seen some really great bonding with some fun father/son time away from screens and nonsense. Looking forward to taking my kids one day.
Don't be shy, use the search function but do ask any questions you have.