Hi, GTR and welcome to the hobby!
Lots of good questions and I suspect you’ll get just as many different answers - it’s a very diverse hobby. Anyway, here are my views:
if you can, come along to the Slot Car Festival at Gaydon on May 20-21. You’ll see a marvellous range of all kinds of new and used slot cars, parts and tracks and many of the vendors, too.
I started out with analogue Scalextric and I still have plenty of their cars. You can’t beat them for price and availability in UK. I’m afraid you’ll find the performance of the different types of cars is all pretty similar, although F1 cars tend to have an edge because they are so light, wide and low. I hardly dare mention the word ‘magnet’ because people on this forum have such strong views. However, cars with magnets are generally much faster than those without, but there is a view that magnet cars are too easy to drive. Scalextric cars generally have very simple chassis and don’t work well if you take out the magnets.
I’ve played with digital at past Gaydon and, last Christmas, I paid £25 for a Scalextric digital set from a charity shop. I have to say it doesn’t excite me as a solo racer, especially when all it has is lane-changers on the straights. The Scalextric digital system is not electrically compatible with their analogue cars and it costs about £20 per car to add a digital chip.
I moved on from Scalextric cars after a while, to the more-sophisticated cars from Slot.It and NSR, still with magnets. With these cars, I began to find the Scalextric track too bumpy and narrow, so I switched to the new-ish Policar track when it became available. I’ve been delighted with it. I did consider Carrera but, like you, I struggled to find in here in post-Brexit UK. Policar sell a starter set without cars and also a basic set with a couple of basic Subaru cars. I bought the set without cars because I already had plenty of cars! My track is small and I use a Carrera lap timer to do time trials of single cars. Recently, I’ve started experimenting with Policar Classic F1 cars without magnets an I find them a delight to build and drive.
In case you haven’t already discovered, Pendle Slot Racing are probably the leading online supplier for UK. I’ve also used Gaugemaster, who I think are the UK agents for Policar, and Jadlam, among others. Gaugemaster have the Policar starter set in stock at the moment. (Search results for: 'policar starter set' | Gaugemaster
I’ve done my usual trick of writing too much and I see driver#8 has posted while I’ve been writing! I’d better finish by endorsing what driver#8 says: enjoy it!