Going to have a dedicated line installed- What should i know to ask for?

The NEC is the National Electrical Code in the U.S. Covers every state. Personally, I’d run 12 wire for 20amps, rather than 14, there’s virtually no difference in the price of the material, compared to the job as a whole. Beyond that, I’ve no idea about audiophile grade connections, etc. Do your research ahead of time, or let the electrician know your plans/wishes before he’s on site, not after.This all presumes that it’s even possible to install a dedicated circuit in an old building like you describe. You may be downstream of other sub-panels, and the like. Georgehifi, ground clamps on water pipes are frowned upon in the NEC, have been for years, even though thousands still exist. Anything new almost always gets modern 10’ ground rods driven into the earth, and in pairs. Too much old iron plumbing has been replaced in pieces with plastic, disconnecting the electrical grounds. You may already know this, of course. Also, at least in the part of the U.S. that I'm familiar with, electricians don't work on any part of the service upstream of the meter, such as the "drops". Those are done by the local utility district. And as a disclaimer, I’m not an electrician. Good luck.

Sometimes, it's just a matter of luck. Our house was built in 1952, the original wiring was two-wire, w/o ground. The boxes are all metal, and are (from all I've seen) grounded separately from the circuits. It's dead quiet, zero hum.  In the twenty years we've been here, we've replaced the fuse boxes with a modern breaker panel, replaced the original meter with a 400A meter socket, re-did the service drop, replaced much of the old two-wire with modern Romex w/ground, as I've been able during remodels, etc. It was a fairly basic arrangement, done well (for the time), and wasn't ever botched up.My only caution to anyone would be to have the work professionally done, if you aren't certain what you're doing. Goes double, if you're in a multi-family dwelling.