About film speed.
I prefer a medium speed film, about ISO-100.
The reason is, with ISO-400 film, in daylight you will turn your adjustable camera into a box camera. f/16 @ 1/500 sec. That does not give me much if any room to adjust speed or aperture. My MF camera only goes up to 1/500 sec, so I am stuck at ONE exposure setting, w/o using a ND filter.
If you have a camera with a film back (Hasselblad, Bronica, etc), load up one back with ISO-100 film and another with ISO-400 film. Then use the appropriate film for the lighting condition.

About the film, you may not have much choice. Check out what they have at your local camera shop. That would really be your limiting factor, unless you mail order your film. I was very disappointed today. The only 4x5 slide film the camera shop had was Fuji Velvia 50 and 100, no un-enhanced contrast film. Talk about having no selection to choose from.