I want to bypass my filter and softner on my well system for outside water use. I was going to tee off on the main line coming from the well. Is this OK? Can I still expect good pressure?

Sounds doable and pressure should be even higher than what is going into the house after the filter.

Yes. As long as you position the tee behind the pump discharge and as long as it is in front of everything else.
There maybe a problem with this if you have an overload of silt and dirt coming from the well.
Good luck, Tom

Make sure you don't have a checkvalve between the T and the pressure tank.