A retro-reflective screen throws light back directly towards the projector, just like the reflective coating on highway signs. The traditional material for these kinds of screens is tiny beads of glass (just like road signs). They work best for situations where the height of the projector lens is about the same as the height of the viewer . . . so they're the usual choice for general-purpose classroom and conference-room applications, where one usually just plops the projector on a table.
An angular-reflective screen is designed to be used where the vertical angle to the projection lens is the complement of the vertical viewing angle. They're generally used with ceiling-mounted projectors, because the projector is much higher than the viewers, and the height of the (center of the) screen is somewhere in between. Most modern high-performance screen materials are angular-reflective.
Both of these attributes have to do with the "gain" of the screen, which is a measurement of how directional it's reflection characteristics are . . . kinda similar to how directional a speaker is. A perfectly matte-white surface is considered to have neutral gain (gain of 1.0), that is, it's both retro-reflective and angular-reflective to exactly the same degree, and reflects absolutely all of the light that hits it. Screens with a gain higher than 1.0 increase brightness (and contrast) by sending more light in a particular direction . . . provided, of course, that it's in the direction of the people watching it. If it's the opposite direction (wrong screen choice) then it DECREASES brightness and contrast. Gains of 1.3 to 2.0 are typical for front-projection home theaters.
There's also the matter of the grey coatings used on some screens - what they do is improve black levels by absorbing some of the ambient room light. Of course, the screen doesn't differentiate between room light and projector light, and a coating like Stewart's "Greyhawk" actually has a gain of less than 1.0 . . . I think it's about 0.8. This is a good screen for applications where you're making up for the loss in light by spending more money for a brighter projector. On the other hand, Stewart's "Firehawk" coating is grey and has a gain of 1.3, so it "gooses up" both the black levels and the brightness . . . making it a great choice for a more budget-oriented home theater. The tradeoff with Firehawk is viewing angle (nothing is free) . . . so you definately need to get the projection geometery set up optimally to get your money's worth out of the screen.
The other benefit of a gain screen is (when set up correctly) if the ambient room light comes from a different direction than the projected image, you get double the benefit, because the ambient room light isn't reflected towards the viewers. So in a typical home theater, the WORST place to have an ambient light source is directly behind the seating area. And for an angular-reflective screen and ceiling-mounted projector, recessed lighting (with BLACK trims) is definately the way to go, as this reduces glare from a critical direction, if the lights are to be used at all with a picture on the screen.
And finally for your application, you have to be concerned with the opacity of the screen, because you're also using it as a shade to block out room light. This is an area where many of the cheaper screens have problems . . . and it's also not usually possible to mount the screen so close to the windows that this really works very well. Usually these windows will require shades as well.
Oh and your screen-size choices are refreshingly sensible for a budget theater . . . I can't tell you how many times I've seen people try to use a $1200 Powerpoint-grade projector on a 120" screen with ambient room light, and then come to the conclusion that "projection looks bad". Go figure.
