Looking good, mate. Just be sure to check the fit in your chassis - you don't want that bar to foul the input jack tips. By the looks, you shoild be fine but it is always good to check. I reckon one of those solder tags will suffice for support. Pop it in the middle of the long span. You have used good, stout wire for the turret connections so it will be nice and solid. Regarding the preamp DC supply, under the board is neater IMHO and should not pose any issues if you bring the wire up through the turret and hook it over the top (like an upside-down J). This way, you can change components on the board without fear of the wire droping out.