Hi there cheetah,
A couple of things to think on...
1. With BIAB, you should aim at a normal crush. A very fine crush will not give you a stuck sparge but it will give you more trub that you will have to deal with later and also a very slow draining bag. A fine crush is not something we should strive for in BIAB.
2. My good mate Ralph has said that many BIABers use coffee grinders. I am going to ring him and ask him who???

. I have read, very occasionally, of an all-grainer (traditional more than BIABers) using a coffee grinder. It is rare, not common. If you want to crush 5 kgs of grain you definitely don't want to use a coffee grinder. For a start, it will take you ages.
3. A mill is an expensive bit of gear. If hand-driven, a small mill can be laborious to use. A good quality mill takes a lot of thought and some money to set up. It also takes space so...
Don't rush into buying and storing your own grain...
People will tell you that grain lasts forever but the specs give malted grain a best used by date of 6 months if stored correctly. Depending on what beers you brew, you might need to carry two or three base malts and around 10 specialty malts. Often you'll find that you run out of a malt and need to get some malt mailed or take a run to the home brew shop to top up costing you $5 in petrol.
What I am saying is that storing your own grain is great but if I was forced to remove one aspect of my brewing from my home, then the first thing to go would be my stored grains and mill even though I love them. They are definitely not a necessity.
The most expensive ingredient in brewing is your time. A few extra dollars spent on buying grain as and when you need it might well offset the hidden costs of storing your own grains. (Some shops will crush your recipe and mail it to you in vacuum sealed bags.)
Obviously, there are many situations where storing your own grains is the most sensible way to go. I think though that a brewer should not be storing any malt until they have bought a decent mill.
Hope that makes some sense cheetah
Cheers,
PP
P.S. This post
here might be of use as well.
If you have found
the above or anything else of value on BIABrewer.info, consider supporting us by
getting some BIPs!