Take it all back to brick work, paint sbr bond onto brickwork, render around all the brick work, moisture proof plaster board (green board) using dry wall adhesive (dot and dab), plaster window wall, after plaster dries seal window with silicone or mastic. hope this helps you.
Yes and no, rendering should be done straight away or at least 1 coat of render to water proof building as water can penetrate through existing walls, there is no actual time limit but it does depend on water penetration.
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