I can understand you wanting to comit to a more structured programme in order to continue enjoying cycling. Training indoors has always been good for avoiding bad weather and doing a bit of intensity. Its easy (for me) to get carried away and do too many short hard/ hardish sessions indoors. Much harder to do longer, easier work indoors (I get bored).
My feeling would be that put simply, to transition into regular trainng and reach your goals you need one hard session each week on the trainer, possibly go to the gym and do some core/legwork, then add more moderate sessions indoor or out and see if you can achieve 5-7 hours per week consistently.
Rest every 4th week at least – reduce vol and intensity.
How to achieve this? I think it definitely helps to have a training plan, even if you are not racing. Define objectives so that you have clear events to work towards. I use the workout builder in Trainerroad, but then end up swapping out the endurance sessions for group rides on Zwift. Sometimes I swap out harder sessions for Zwift races. Sometimes I do no training for 2 weeks and drink beer. I’ve not had a coach before. I think if I was coached there would be more pressure to train and I dont necessarily need that. I’m generally reasonably well motivated and if I dont want to workout I just reckon that I need a rest.