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A 3/4 HP should be fine for your pool to circulate water. Often times it's more important to match the pump HP to the filter size so that they compliment each other. If you get a variable speed motor, you can get a strong one and simply adjust the rpm lower as needed. Most sand filters come with a standard multiport valve (MPV), so I'm a bit usure of this 4-way valve you are referring to.

What make/model pump/filter are you looking at? Also remember that you don't have to get an Intex pump/filter. You could go with various other makes & models. The only thing about that though is that Intex uses proprietary fittings that are about 1.25" or 40mm in size, where as most other pumps/filters use 1.5" or 2" fittings. So you would have to use some adapters to get them to make-up together.