Why not just use firefox profiles ?
for two, I don't know anything about Firefox profiles, does that create a profile for my extensions too? Will multiple firefox profiles have different metamask instances segregated?
As with Firefox, the profiles are completely disconnected, and have different history, extensions, cookies, etc.
If you don't like Chrome's resource hogging, try something like The Great Suspender.
I've started using them recently to have entirely seperate environments for personal and work websites and it's a blessing. Previously I used 2 browsers just like you, now I have the unlimited power of Firefox AdBlockers in every environment.