Where do I start?

Join a club and go for some group rides through the winter, enter some local TTs they're always a good way to start racing IMO. Enter a crit race but don't worry if you get dropped the first time, speeds are usually about 25mph but there can be big surges in pace that catch people out. Have fun and don't crash.

25mph sounds high but in a group it much easier, it's the surges in pace that are harder to deal with. Silver BC membership gives you a prov race licence which will do for most crits and road races.

Start with club chain gangs and TTs. Do some turbo sessions over the winter.

Before having a go at mass start racing you could try a time-trial (tt) as this may give you a measure of where your fitness is. Throughout the season many clubs run 'club' 10 mile tts. You can turn up on the night (usually mid week)and ride for a couple of pounds, most will let you ride once to see if you like it before you need to join an affiliated club.

With respect to road racing try a closed circuit race (on an airfield or motor circuit) preferably 4th cat only if you can find it or if not 3/4. For this you should be able to enter on the day but may need to pay extra for a day licence. Do not turn up in your Sky jersey/shorts. For a BC event you can only wear the clothing of the club you are in or 'plain' jersey and shorts, sames true of an open time trial.

There is no requirement to join a club even if you do take the plunge and get full BC membership (silver or gold) and a racing licence you can join BC as a private member. However, I would recommend that you do join a club for a huge range of benefits. Training partners, learning to ride on a clubrun or chain gang, sharing lifts to races advice.....etc. Also no clubs = no races.

Pretty sure that 4th cats can wear trade team kit if they want and whilst full Sky kit may attract a few comments you do get people turning up in trade kit so don't worry about that until you reach 3rd cat.

I wouldn't be scared of entering open road instead of closed circuit as your first race either - not if you've taken the advice to train with racers over winter/spring.

Closed circuit crits are generally less forgiving of novices as they are more technical and if you end up at the back of the bunch you'll be sprinting full gas out of every corner - something you can only do for so long before getting dropped. Open road events are generally easier to stay in the bunch unless they are very hilly - plus in some areas the first races of the season can attract over 100 riders on closed circuits making for some fairly hairy moments in the bunch.

I was new to racing this summer, after a couple of winters of club runs and summer sportive campaigns.

First race was a proper Cat 3/4 Crit in York - Bad idea. Off the back almost immediately and lapped shortly afterwards. Not the first to be lapped, but still not ideal! Although I am a bit of a sprinter, the constant surges in pace were too much.

Second race was a 4th cat only at Dishforth airfield - Much more like it. Average speed was 41kmh for 40 minutes, which is much faster than my usual solo riding pace. (I'd typically manage 33kmh for an hour on a flattish route with a few junctions.) If you can follow wheels safely, you don't need to be Superman to stick with the bunch, though unless you can sprint, or at least inject a bit of pace for a minute or so, you'll not be at the sharp end come the finish.

Re "following wheels", I can't recommend highly enough riding with a club, preferably one with a few old hands to keep you on the straight and narrow! It's not rocket-science, but you do need regular practice to keep your technique polished so you ride safely and efficiently. Every time I have a few weeks off club runs, I am all over the place for the first few minutes on my return, until I've reremembered what to do. You don't want to experience this feeling in a race!

If you can ride with a club that is better than you then so much the better. My club mates routinely work me over as if they are the Kray Twins' hencemen, and I rarely avoid getting dropped, but this still left me very competitive in the flat Cat 4 only race at Dishforth.

Even if you don't race much, riding in slick "chain gang formation" with 10-15 club-mates at the weekend is a very enjoyble feeling.

Re kit - Although I'm a member of a club, I've just raced in a bog-standard black and red jersey. Most folk are in club kit, though.

Re equipment - The Cat 4 crowd would appear to generally just turn up on their normal summer bike. Fancy wheels didn't seem to be too prevalent at Cat 3 either, though there were a few. Cat 2 was a different matter, though.

Silver BC licence.
Find a race.
Go race.

See how you do. It's fun. You'll get better.