I'm not an expert but I might be able to help.
More than twice a week? No you shouldn't, you need time to rest and recover.
I tend to do different intervals for different reasons. I usually will adjust my recovery rate. If I'm pushing my legs to their limit, I'll give them time to recover, so for every minute of work I give 3 minutes of recovery. If I'm working aerobic intervals then I'll use a 1:1 ratio but I obviously don't push as much power.
Instead of deciding on increasing length over speed over number of intervals. Why don't you opt for doing something like 6x5min intervals one day. Then do 3x10min intervals another day. Your work should be the same in both instances, but your training in different ways. On my road bike I llike to do pyramid intervals, you work for 1, 2, 3, 4, 3, 2, 1 minutes. The recovery ratio I vary depending on how I'm doing them, this seems to work well for me.
As I said, no expert here, but this might help.
More than twice a week? No you shouldn't, you need time to rest and recover.
I tend to do different intervals for different reasons. I usually will adjust my recovery rate. If I'm pushing my legs to their limit, I'll give them time to recover, so for every minute of work I give 3 minutes of recovery. If I'm working aerobic intervals then I'll use a 1:1 ratio but I obviously don't push as much power.
Instead of deciding on increasing length over speed over number of intervals. Why don't you opt for doing something like 6x5min intervals one day. Then do 3x10min intervals another day. Your work should be the same in both instances, but your training in different ways. On my road bike I llike to do pyramid intervals, you work for 1, 2, 3, 4, 3, 2, 1 minutes. The recovery ratio I vary depending on how I'm doing them, this seems to work well for me.
As I said, no expert here, but this might help.