Quite a lot of zone 2, couple of steady state intervals per week for quite a lot of it. Increasing from 2x10 min - 3x12min over a couple of weeks. By week 6 I was doing 2x20 minutes steady state intervals.
Coming towards the end of the program there have been more VO2 intervals 3x4min and 4x4 min. Finally a couple of sessions of "speed intervals" which are basically 30s efforts at max power win minimal rest.
Its not a complex plan, its just that going back to 2x10 min steady state will be easy after 2x20min.
I think you're thinking along the right lines. If those sessions were starting to feel comfortable at your current FTP then you won't get anything out of going back to week 1. I'm assuming your steady state intervals are around sweet spot intensity (i.e. c90%). Let me know if not.
If you've got time for 5 sessions a week, at this stage of the year for all round fitness I would probably be doing something like:
Mon - rest
Tues - either 90-120 mins Z2 or an hour varying high Z2/low Z3 (75-85%)
Weds - longer interval session - 4x15 min @ 88-92%. Goal is to progress this to 1x60 min. Try 4x15 > 3x20 > 2x30 > 1x60
Thu - rest or optional easy spin
Fri - shorter interval session - 4x4 @ VO2 aiming for maximum sustainable power across the sets
Sat - 2-3hr endurance
Sun - 2-3hr endurance
Ideally the weekend rides would be outside and I'd make one hillier. The suggested duration is not fixed if that represents a big step up in your training load. Similarly, if you're time crunched on the weekend I'd do another longer interval session in place of one of the endurance rides. As an example, I'd do something like 1hr around 80-85% and every 5 mins up your cadence by 10rpm for 30 seconds aiming to push above threshold.
Those 30s intervals are useful but I really see them as an "icing the cake" session rather than a regular session. I've done them in the past 2-3 weeks out from a big event as they do give you a real boost in the short term, but aren't sustainable mentally or physically in the long run if you're doing them all out.