If this is intended to be an acceptable egress opening when you go to sell, check to make sure the window is approved for egress and has a large enough clear opening. There is also a require for the bottom of the opening to be either 42" or 44" MAXIMUM above the floor( the actual dimension can vary from area to area). This requirement is to allow children to get out and the opening is to make sure a firefighter with gear can get inside to stop the fire.
Depending on your exterior, you may need an access pit large enough for a firefighter with gear to get into.
If it is not acceptable ans an approved egress, the person make the appraisal for selling may not include the basement as finished space, so valuation will be lower and the amount of financing will be less and the potential buyer will be less.
Lay out the masonry opening required and cut the opening with a saw or hammer and chisel. Using treated wood, make a set of wood bucks (masonry nails into the block) to create the window's rough opening. Install the window after shimmed and fill any voids with non expanding foam.
Once you have the masonry opening determined, you will know how much room you have up to the sill. You have to find someone to determine what kind or header you may need, depending on the opening width and the load on the window area from above.
It takes some planning and sketches before you start knocking a hole in the basement wall.