I have 6 jl 770 wired to a 500/5 amp. 4 speaker going to to 100x2 channel and 2 going to the 2x25 channel and 2 subs going to the 250x1 here is the questions.

1. I have a 300x4 jl amp can I wire 1 to each channel and bridge one to 1/2 channel and one to 3/4 channel?
2. Can I wire mids to the sub channel on the 500/5 amp.

1: if you are only running one speaker to 1/2 bridged and another to 3/4 bridged then yes you'll be able to do it. But of you're running 2 speakers to the bridge then no because it will be seeing 2ohms the amp is only stable to 3ohm bridged. However if you are only running one speaker to each bridge you won't see a full 150watts to it because is not at 3ohms
2: only if the amp has a "mid pass filter" on that channel. I doubt it does.

It sounds like you are trying to piece this together without spending a lot of cash. My opinion would be to buy the right amp to power the speakers and save those for another project. They will either fry or be underpowered.

Describe what you are trying to do with your system and I'm sure someone will chime in with some good ideas