Although I have no experience with fruiting bushes or trees, I just happen to have read some info, last night, about the soil needs for containered fruits that said that they should be given new soil every two years, with a heavy mulching around the bush every fall. I also learned, a while ago, that, on average, the amount of roots below are approximately two thirds of the amount of plant you can see above ground. (Ex. If you have a 3 X 3 plant, you probably have 2 X 2 roots below.) Also, with most plants, it isn't any better to have them in a pot that's way too big, then it is to have them in a pot too small. (The book I read that in, never told why that is.) I know that doesn't answer most of your questions, but hopefully others will add to this thread until you get all the answers you need.

Not only would I suggest that you stick with the 5-1-1 mix, especially if your plants are healthy and happy, I'd go so far as to say that a repot probably isn't even strictly necessary at this point. Here's why: fabric pots function more like raised beds than containers (that is, as long as they're in direct contact with the ground/soil). That means that, even if your mix has compacted as it has broken down, your fabric pots won't support a perched water table in the same way that plastic will. Also, fabric pots encourage branching rather than circling roots, which helps to prevent plants from becoming root bound (or at least slows the process down). Furthermore, blueberries' fine, net-like root systems aren't all that prone to circling anyway (or, at least, that's been my experience), so the combination of fabric pot + blueberry gives you more latitude than you'd have with other plants and pots. That's not say that root maintenance is a bad idea, especially if you noticed any signs of flagging growth or stagnation. Rather, I'm merely suggesting that it's not necessarily a "must do" at this point. However, if you do decide to bare root and repot them, then I'd stick with the 5-1-1 mix or something similar. If you want a mix that's suitable for fabric pots and that will also hold its structure longer term, then I think I recall Al recently recommending something like 3 parts screened park to 2 parts turface. I haven't tried it, but I suspect that the standard gritty mix would drain too well and dry out too quickly in fabric pots.

All my blueberries are in the ground but I would think your blueberry pots are "crowded". The answer would be go to a bigger pot but that is not possible for you. In your situation you will need to water often because there is not enough soil to hold much moisture. Use slow release fertilizer and water daily. Use the smaller chipped pine bark mulch to help hold moisture.

Fruit production is in direct proportion to health and growth. The more limbs you have the more fruit you will get but that is not always a good thing as BB tend to over produce which is bad for the plants. Some BB do create flowers toward fall but the berries never get very good and I just pinch them off. It is a sign the plants are doing well ( IMHO). Not all varieties produce the fall flowers. Basically just do all you can to make the plants put on a lot of good vigorous growth.