It’s like at photographer’s - sit down, chin up, smile, don’t move, here you go. Nothing can move while F12 render frame happens.
You can move things (including Camera) around while in preview render mode though. To have camera “see” what you see on the screen hit Ctrl-Alt-zero key on numpad. Sometimes Camera jumps too close- select Camera hit G and press/release middle mouse button. Slide mouse forth/back to position as you need. If you now rotate Scene view will go away from camera view - hit 0 on numpad to see through camera again.
To your wall. I’d say go for it one more time. Set background image, Ortho view (numpad 5) and add Plane. Switch to wireframe mode. Move plane to start from the lower left corner of the wall image; move x 2 right vertices so that plane covers first opening. There are two of them - you can reuse one you will make. Use Ctrl-R to make two loopcuts and if plane was symmetrical from the middle of the first opening while in adjustment you can scale loops to get where widest part of the opening is. Add two more loops and position edges so that width is the same as the top part of the opening. Make two loops across.
Now you have all the needed vertices to form opening - move on x middle edges (you can select two and Scale apart). See if you have vertices for the top, if not, make loopcuts (Ctrl-R) again. Select needed edges at the top - e to extrude.
One part is done - select all verts and Shift-D, X to copy and move next opening.
Select rightmost vertical edges and extrude to where central part starts.
Select upper vertex and Ctrl-mouse click, tracing the top part. Select traced vertices and e extrude Y. Scale SY0 to get flat line.
To get horizontal lines use K knife. KC will draw strictly horizontal lines; cross all and hit Enter.
To be sure remove doubles (w - Remove Doubles) and Ctrl-N make normals consistent.
Select right lower vertex and Shift-S cursor to selected, Switch Object mode and on Toolshelf Set Origin to 3D cursor.
Now you can UV unwrap from view add materials, texture and Mirror modifier - this will take care of the right part of the wall.
Surely takes less time than write this :).