How important is a flex pipe in the exhaust system if you have solid steel motor mounts? I'm wondering if I can do away with it but I don't want to put any unneeded stress on the turbo or the manifold.

I flexpipe is VERY important on a FWD car. My old blue car didn't have one when I first got it, and even with filled motor mounts it chattered and cracked the exhaust in a week. Spend the money and get one.

Even with solid mounts the engine still moves. Without any give in the exhaust track something has to move, and that will end up as an exhaust leak.

Guys the OP said "solid steel motor mounts" as in zero motion of the engine is possible. In that case, you will have maximum NVH in the car and a flex pipe would not be required.

Solid steel motor mounts don't eliminate inertia all together. In a FWD, front engine car a flex pipe(s) is mandatory is my opinion.

I'd say yes, or the first time anything snags on your muffler, it's a broken header instead of a slightly scratched muffler

If you have all four mounts as solid steel then a flex pipe would not be required. Your car will vibrate like an unbalanced washing machine....lol

from experience from a guy who tired going without a flex pipe; i would say just put one on just in case. i ran w/o one and it didn't last long i even had a extra exhaust mount welded on the pipe and that didn't do shit.

100% NOT optional. You need a flex pipe. Period.