Replace the cabin filter (10 minute job) with a carbon activated one. I find it makes a big difference on longer drives, otherwise my nose/throat are awful.
Don't worry about the ticking sound the engine makes when it's cold, that's normal.
Check what the tyres are like (age from the DOT code, and tread).
When you're feeling flush, I recommend getting all-season tyres, Goodyear Vector 4 have served me well.
Upgrading the speakers is not difficult, and makes a big difference. (At least under 50mph, lol). The door speakers need to be under a certain depth, or the windows won't go down.
If you want CarPlay/Android auto, the fitting kit for a standard 2-din unit is about £25, and a half-decent unit is about £200 (Sony xav-3250).
Imo, it's well worth getting some good cleaning supplies.
A good shampoo to get it clean (I like megiuars gold class), then a sealant to keep it clean longer (meguiars ultimate ~~sealant~~ wax, comes with applicators too).
Wash with the two bucket method, and a couple of microfibre mitts.
Get a dashcam as soon as you can reasonably afford one, and set it up.
I like the Viofo A129 duo, it's basically invisible behind the mirror.
Halfords have this one on special if you don't want to spend that much:
On the actual driving side, once you've had a bit of time getting used to driving, buy yourself a copy of Roadcraft, and have a good read through of the advanced techniques, particularly IPSGA, the Car Control system, and limit points.
Learn to drive defensively, and you'll avoid a lot of sticky situations entirely, rather than having to suddenly do things.
Sometimes, you just have to let dickhead drivers be dickheads: You may be in the right, but if you crash you're both in an accident.
I started looking into non-carplay/auto big-screen head units when I bought mine, and kinda hit a wall on it.
They're either really old, and windows CE, or shitty android based ones from alibaba.
As much as I hate putting myself into a system that depends on my phone, I don't hate androidauto/carplay based systems. They just kinda...work.
If you just want a basic head unit (single din), the name brands are, honestly, much of a muchness.
They all use very similar 4x50w (iirc, 22w rms) output amplifiers.
The only real options are number of pre-outs (for connecting subwoofers, or other amplifiers), and whether or not it has a CD drive.