BP Farming Startegy

You usually farm candies in preparation for the event as to not waste resources during the actual event.
With a decent deck, you should at least be able to bring their health bar halfway using 2 BP if you're aiming to get MVP. In other cases, you can either just initiate the festival with 1 BP and hope someone defeats it for you.

Since BP regens at a rate of 30 min/BP, you'll want to always use the BP before you reach 5 BP capacity, as this will reset your regen timer. It's best to start using your BP once you reach 4/5 to keep the regen timer from resetting.
How I used to do it was set a reminder for two hours after I had completed my rounds. I can usually get through 2 through 4 festivals per round, depending on how lucky I get with the BP Chance.

In order to maximize BP and Genki, I would go through the promotion until I get my first festival. Once I get my festival, I use 2 BP and call for help. If no one helps in 5 minutes, I usually just defeat it myself using an alt. After that festival is done, I run through the promotion again until I get another festival. This time your actions depend on if you got any BP chance or not. I hit with 2 BP and call for help if I did get BP(Option A), or I hit it with 1 BP if I didn't get BP and call for help(Option B).

(A) If you were lucky enough to get BP by the 2nd festival, wait until someone kills it or kill it yourself if too much time passes. I usually do a bit of promotions to see if I can get anymore BP between the time the festival starts and before I beat it, but don't push your Genki too far down, as you want to save enough for a potential 3rd and 4th festival (depending on how much BP you got left).

(B) If you didn't get BP at this point, you're goal is to now do Promotion until you do get BP. If you don't get anymore, just kill it using 2 more BP (One from reserves and one from current capacity; You'll gain back the reserve Candy after beating it). If someone is nice enough to kill if for you, you'll have another single BP to use for a 3rd Festival. If you do get BP at any point, refer to Option A.

At this point, if you have some left over Genki and not enough BP to finish another Festival, DO NOT continue promoting. You don't want to get in a situation where you can't complete a festival without using more than 1 Candy.

Alternatively, you can just be cheap and try to only spend 1 BP per festival, but I find this an unreliable method that'll lose you a lot of fans if they're not getting completed. and it's slow.

Note: If you happen to get a BP Chance that will increase your BP past your limit, (i.e. I have 3/5 currently, and then I get a 3 BP Chance), don't click confirm on the BP Chance page and open a new tab of ML. Go ahead complete your own festival if you do have one up. If you don't, help out someone who does. Now you are safe to confirm the BP Chance  and you'll get all your BP.
The same can be said for leveling up, however it works a bit differently than the BP Chance. No matter what, you can not get to the level up screen if you want to use up any resources before leveling up. If I see I'm close to leveling up and I still have BP left with no festival active, I reroll the promotion to the point right before I level up until I do get a Festival.