I have had this crash happen once myself. On your 4 crashes did you lay a power bomb each time? I think it happens if you lay a powerbomb and then run into an enemy in the room at the same time as the explosion goes off but Im not 100% sure.
Heres a video of when I had it crash on me. It looks like I ran into the enemy at the same time the explosion would have killed him maybe? Not sure though
Digital installed onto switches internal memory. You also save a bit of time if you remove your SD card all together. Version 1.0 is also a bit faster than 1.01 but most people are running on version 1.01
Original n64 controllers are the best in my personal opinion. I have and do use a hori(for throws only) but I know lots of people use it for full runs. I personally prefer the original controller as that's what I'm used to.
One of my buddy's uses a gamecube controller with an adapter and he loves it. I personally think that the C buttons are much more consistent and user friendly than a c stick for setting up angles, but that's just my personal preference. Third party controllers are generally unusable.
I buy all my controllers off ebay. Be careful with which ones you buy though as lots of the used ones are pretty shit. Depending on your budget you can usually find a new in box controller for around 150$. If you want to extend the life of controllers, use a hori for throws.
BLJs are very hard to be consistent at and I would argue that there is no real way to actually be consistent. I have found that hitting the stairs at a slight angle and trying to start the mash as soon as mario makes contact with the stairs helps some. but really you just gotta get a feel for them. Also when you do the blj to get to BitS, be very careful to not angle to the left or there is a high chance you will clip into WDW (learned that the hard way)