I am remodeling my house and want to add steam room feature to my 8’x4’ shower area. I have a few questions that I would love to hear your wisdom.

1. The shower space is 256 cubic feet and I got a great deal on a machine that is designed to serve a room max 225 cubic feet. Will this be a problem for the system being undersized? Could I bring in a 2x2x6 box as a bench that would take up 24 cubic feet of volume to help?

2. I have 2 windows in the shower, they are being replaced with 2 milgard vinyl double pane single hung windows.  What should I do the properly seal the old aluminum frame or the new retrofit window so that moisture won’t penetrate? For example should I silicone fill all the gap in the old aluminum frame before I install the retrofit window on top of them?