However the pack will fully support the MultiMC launcher, you can make your own instance definition in it to distribute.
But yeah, will need to ask those other mod authors if it is okay.
Forge uses ASM heavily, and I think FML does too. They are generally the prime examples of how to use it. I have seen another mod that used it too. Quite powerful, lets you change anything at load time.
Basically by using ASM your mod will become a coremod instead of a mod.
Forge itself is open source so you are welcome.
As for the individual mods, you will need to ask their authors.
Do note that FTB is making a mod pack and will have support for other maps, so if the mods that you need to use are in the FTB Mod Pack then you can just use it when it is released soon.
Base edits are now completely unsupported in forge because anything that you would have done a base edit for can either be done with reflection or with ASM in Forge, hence, no reason for base edits any longer.
I think that is correct yes.
Forge currently uses either a registration system or a hook system, depending on what is more appropriate.
Also, get rid of your base edits, they are completely unnecessary now.
And I gave you modder rank with all abilities thereof.
You likely have an old version of forge, get the latest and try again?
Also, post the *full* log next time (in spoiler tags), the rest of the information is also useful.