As a molder, I have seen family molds work but it it VERY rare. If you want to save tooling costs for low production volumes I suggest that you look into modular molds like a master unit die.
PC to PC bond is VERY good. It has exceptional weld strength and sealing. I have previous experience in two-shot molding polycarbonate to polycarbonate. There are some basic rules that need to be adhered to but it works quite well.
A slight increase in shrinkage from the primary part may occur...
I would really have to see your part to suggest a rib pattern. But X patterns generally work well. Make sure that the rib thickness is about 1/3 the thickness of the part wall. to reduce the appearance of "sink" witness in the part.
Use of oil has its own set of problems. It is much lower in thermal conductivity, very messy and dangerous, tends to creep leak from tooling, and it is generally a source of part contamination. It should be used as a last resort for resins requiring very high mold temperatures.
If you have...
Texturing tools can be done with several methods. The actual method depends on the required grain pattern.
Simple uniform "sand" grains can be accomplished with an EDM process during production of the mold cavity.
When this method is not feasible the grain is produced by air brush application...