Hi mfarris, the mini-mill mods will depend on how your machine behave, as you know, this is china stuff, and the quality of the machine can vary a lot between one and other.
Also will depend in your quest for accuracy.
One of the problems for the mini-mill desing is the tilting column, its rarely used and the pivot union at the base is not robust enough, is like a weak point, if you attach a dial indicator from the table to measure the head movement, you can pull by hand the head an see the amount of column flex in the dial, most of that is caused by the weak pivot union.
For light work, brass or aluminium, and with light cuts, I think is not necesary to worry about this, but some peoble cant live with this
and attach a steel plate in the back of the column as you have seen in so many mini-mills mod threads.
gib adjusment is also necesary, in some cases there is imposible to get the gibs rigth, and new gibs needs to be made.
Other thing, this I will say is a must, is the belt-drive mod, as gears are from plastic (I dont know if new models have the gears made form metal now
) and will broke at the first jamming, also the mill will run more quiet.
Other peoble fill their columns and casting with a dense resine to reduce vibration.
Also they change the the head spring arm for some air sping.
Some put DRO...
You will find that the Z axis is very tricky, and a DRO or a dial indicator will be a must to add also.
Depend on you and your machine what mods are necesary and what are not, I say a belt-drive and a dial indicator or DRO in the z axis is what you need to consider as started.
Hope to help
Saludos