If you are doing single shots, go with the wider. Inside you cannot always step back far enough--why do rooms always have four walls. 25mm equivalent is actually good for interiors as I find even 28mm tight.
As far as the minimum aperture, I would up to f/16 without hesitation. Having the DoF you need will always produce a sharper image than what the effects of diffraction can do--shoot a few frames wider if you like, but f/16 will be really nice. Personally, I would even go to f/22 in some cases and the results will still be great for your clients--unsharp masking is your friend here. Your clients don't care about pixel peeping and your format will work really well at f/16-f/22. (f/8-f/11 will not have the DoF for this work. You can also looking into focus stacking and you could shoot a stack as an option.)
If you are still determined about the 45mm, you can stitch two or three frames and shoot the camera vertical. I am not really into lots of stitching for architecture. You will need a nodal slide for interiors, which can easily be done, but it is just another layer. Then you have to account for the projection in the stitch and sometimes that is hard to judge. At this stage I would go for single frames and might try a few shots for a stitch just for the experience, but I would not count on them.