Best bet is join British Cycling. Why? Well it’ll give you a level of insurance. So, if, the worst happens and you get knocked off, you’ll have cover. That’s really important, otherwise you’ll lose a proportion of your claim. It’s important to claim to cover the cost of clothing, kit and bike damage. Also any injuries sustained - loss of earnings and the cost of rehabbing them (I wouldn’t rely on NHS - have you seen the wait times for physio!). Likewise it’ll cover therapy for any psychological trauma. You may of course find that your car, health or home insurance covers this. If so, fair enough. The benefit of joining BC is not just the insurance, but they have a batch of training programmes that you can download. They cover everything from beginner preparing for first sportive, up to seasoned racer wanting to get ready to race.
Don’t cycle outside again until you know you are covered! Cycling U.K. offer the same just for joining them. My partner found this out the hard way. He’d left his BC card at to remind him to renew his membership, forgot, then got knocked off. He lost several thousand quid from his claim having to go through No Win, No fee.
Alternatively programme wise, I wouldn’t shy away from using a wattbike. That’s an awesome resource to have at your disposal - I’m well jealous. I’m a seasoned racer (road, crits, time trials and cyclo cross) and I do the bulk of my training indoors (smart turbo for me). What I would suggest if you don’t go down the British Cycling plan route is using one from Zwift, TrainerRoad or Sufferfest. All you’ll need is a tablet, smart phone or Apple TV/ smart TV that you can station in front of your Wattbike. I use a tablet attached to a cheap music stand off Amazon. Then download your preferred app - they all have free trials, so you can decide which you like best. Zwift has all manner of training programmes which you can sign up for. There’s certainly one on there for what you’ll be looking for. They are ‘free’ as you pay a monthly subscription to use Zwift (£12.99 per month). Each time you do one of the pre-set sessions it adjusts the resistance according to the effort you need to put in and will give you prompts for cadence. Obviously as PP said you do need to HTFU and just get out on the road as often as possible (as long as it’s not icy, snowy or very windy). There’s no such thing as bad weather, just poor kit choices/ poorly equipped bike. Sorry if that sounds harsh. But we’re British cyclists, we’d never blooming ride if we only went out in fine weather (so about three times a year). Also when it comes to event day - what’ll you do if it’s raining?! Best to be in the mindset of just getting on with it and having the best kit to cope, likewise having your bike kitted out to deal with it. Most importantly you’ll be able to handle it on wet roads. It’s actually no biggie, but if you aren’t used to it it could go titsup. Literally.
The other benefit of doing wattbike via a programme is you are less likely to miss a session. Other than illness, there’s literally no excuse. I work full time and have a young child so have a very narrow window to train. I just wouldn’t get chance without the turbo.
Happy peddling. You’ll love it and training is super fun. It’s ace and so motivating having a specific goal to aim for.