Rosemary is a shrub. Sage can be a shrub. Thyme and mint are creepers. I would put the mint in it's own pot. It's really aggressive. Thyme will just hang in with it's buddies. Rosemary will grow huge! Sage can also grow big. Mint is the most aggressive of all. We have mint here on acreage. It's on a dripper. It will not cross a desert to find water. It loves damp.

Agree. Mint is far too aggressive for growing in anything but its own pot - unless you want it to take over the entire 2x8 foot bed. If not a pot then plant it somewhere that you won't mind when it takes it all over.

Too much for sage+thyme+rosemary? Not at all. A bed that size could easily hold many more herb plants unless you are wanting to plant tons of each.

The other issue here is that mint likes much different conditions than the other three. It like more moist, while the other three require very well drained soil. Give it it's own pot--it just doesn't play well with others.

Now, the remaining bed would be ok for the other three. You can try a hardy Arp rosemary that might survive your winter, otherwise you may have to consider it an annual. (Suzy we can just be jealous of the size your rosey can get when it is a perennial). The other two can get large, but 2' square is reasonable for them if you deliberately keep them spreading too far in a couple years when they get that size. Could even keep the thyme smaller and also look at adding some chives, winter savory, tarragon, or sorrel for perennial herbs.