A yellow or red filter will give you more contrast, so whatever sharpness will be lost (negligible in my experience) will be offset by the increased contrast. It's a wash. Orange filters are odd ducklings, at least around here. They change the look of B&W so drastically that I prefer not to use them. Good for portraits maybe. I think they don't add contrast like the yellow and red, so compared to those two, my photos may LOOK less sharp w/ an orange filter.

I've used very cheap filters and very expensive ones, and never saw a cat's whisker of difference between them. As for flare, keep a good hood on the lens and it doesn't matter. Other people may have different experiences, this is mine.