Rainford gobies make nasty messes spitting sand all over. They pick up the sand, filter out the bugs and dump it all over your corals and rockwork.
Keep in mind that if you get a rainford that it's going to eat all your spag. worms and bugs in your sand pretty fast.
If you have a DSB this is problematic. Also problematic if you have bug eaters like Scooter Dragonettes and Mandarins.
I would not go with the rainford. Again, avoid anything with the word 'sand sifting' in it's name or description.
Most shrimp gobies pair up easily with a new goby. Yellow
Watchman gobies are often the easier to pair with the shrimps. PInk and Blue spot watchman, orange stripe watchman are also easy. The Stonigobiops (spelling I'm unsure of off the top of my head) pair up too but they are fairly fragile and need pretty consisten water quality.
Just put the goby in after acclimating and after a few weeks they'll find each other.
Hope that helps.