2) There is no magic, only physics. Wedge is easy to control to any level you can measure- honest. Most other optical issues fall under one of the headings of: time, care or experimentation. Some simply take more than others.
3) BK-7 when applied to concrete tends to fragment, causing grinding/polishing time and expense to double :-)
4) If you are grinding both sides of the "window" you can order the blank-- "plano-plano, fine ground only" and save some money.
I've also been thinking about a "next scope" maybe an off-axis Houghton, classical Cassegrain, refractor? Well, not this summer at any rate.