I'm a new 400 owner as well, so I'm not going to be the authority on 'normal'. So take this all with a grain of salt.
Phono input is definitely quieter than Tuner or Aux on mine... although that is likely a function of turntable and cartridge as well. Are you using Phono Low or Phono High input? I believe Low is appropriate for most MM cartridges? Are you using a grounding wire between the receiver and your turntable - without one, this could explain the hum.
IMO if you are consistently running your receiver above mid volume, it may not be a good fit for you. If that much volume is needed, you should look into much more efficient speakers or a receiver with a lot more power to suit your tastes - this thing is only a somewhat optimistic 25 wpc.
It will sound fine once the tubes get to temperature (a few minutes). Theoretically, they will sound a bit better after being on for a while at operating temperature.
When they serviced it, did they replace most capacitors and the power supply (as per kits like Metalbone's)? If not, there may be more that should be done to get back in proper working order.