The room has a concrete slab floor with a drain, so if there is a water leak, there is no collateral damage.

The entire list of plumbing fixes includes:replace tub drain (mechanism toast plus drain was handyman'd out of code)replace water heaterreplace slop sink faucetreplace 2 sink faucetsbring upstairs 1/2 bath vanity drain to code (straight drop and no vent)move gas range feed to original placement in the house (they had it where the fridge should be and the fridge was a huge french door deal where the eat in location should be)re-run gas feed to dryer (utility co capped the line back towards a main joint)That ends up to be way more than I originally thought but it could have been worse.We pulled up the kitchen floor since someone had put el cheapo vinyl faux laminate down (always a bad choice) on top of old linoleum.

The water discharge backed up but one side did not have a relief access to drain it and when putting it in discovered that there was a crack in the pipe. 

KBR shower pans makes pre made shower pans any size, drain location and other options.

Good guy, has done other drain work for us and has done a great job.  

Also, French Drains are not that expensive to install.  

A single 2" whole is drilled thru the wall for lineset and drain.

If AC drain clogs, who will clean it?

I understand that there should be moisture in the dirt but how wet is too wet and how do I figure out if an interior french drain and sump pump is necessary?

I recently picked up a drain auger and it was cheaper than calling a plumber.