That suit looks great on you, Cox. Flannel gives a bit, however if it's tight I'd mention it. If it's not too much trouble you could send it back with instructions; during fittings I've noticed letting out seams even a half centimeter can make a difference in comfort.
I wear the 0656 trousers all the time with a navy sportcoat, and even though the jacket has patch pockets I'm with Lord Superb and prefer sportcoats to have bolder patters. It would work in a pinch, but would be suboptimal
Would be curious to see some navy SC/0656 trews pics. I imagine it resolves to grey unless viewed at close distance?