Info on jewelry electroplating in silver, gold, imitation rhodium

Greetings,
I am a mech engineer looking to find out all about plating jewelry in silver, gold, and imitation rhodium for manufacturing needs. I will outsource the processing. I make silver jewelry and want to go to silver plating for many products.
Questions:
what are best materials to plate (copper,brass,pewter, others?)
How long will silver plating last,
What do I need to look for to know someone is a good finisher (any special kind of equipment required for best modern techniques? how long should best quality process take for 3-8 gram (finger) rings? etc.)
Where can I find out about imitation rhodium plating and can it be done without nickel. Similarly, what base materials work, how long does it last?

Any leads to quality platers would also be appreciated.
Thank You,
Shawn Collins