No shame in playing it safe!
1) Yes that's normal on the A-1000 - mine wouldn't click with a 77W bulb but did with 100W. I was going to mention this earlier but figured you already knew since you said you'd being playing music on it with the DBT. So if you want the minimum safe bulb, 100W is the answer there.
2) Is normal in my experience, does vary a little from amp to amp. I'm guessing you already replaced C177, C178 (22uF, 220uF)?
3) Let the amp idle for 15-20mins on mains power and check the idle current, sounds like an adjustment mismatch to me. Before you do that, put your multiturn trimpots in for the L/R idle adjustments - I just assumed you put those in since they were on your purchase list, definitely important - the stock single turns are way too touchy for idle adjustment.
4) Is the hum present on the Tuner or Aux inputs or only DAD? Because if so it will likely just be an issue in the DAD wiring path - I'd check solder joints on that RCA and the plug that comes out of the phono board immediately after the RCA connects to the board... you could unplug and plug the DAD wire's other end from the input selector board too and check that socket's solder joints onto the selector board too. Before all that hassle tho, I'd spray some isopropyl into the front of the DAD selector switch, I have found that excess *whatever* in there not drying up can cause a buzz too. If it's *only* that input it will be a minor problem.
Regarding the bias voltages, get those Bourns multiturns in for the idle pots, then re-check.
My A-700s live in Class-A mode, no dramas. These amps are built to handle it, though I feel it takes a good set of speakers to really appreciate the difference. The bias transistors mounted to the heatsink will regulate the values to a more constant (and lower) value after about 30-40mins in my experience. The A values won't stabilise in 2mins. With that said, I do think the amp needs to be built strong to take the heat (hence redoing all the solder joints, recapping, etc).
The switching point adjuster won't have any impact on those bias voltages either, it only affects what happens when the amp would clip in Class-A mode (~10-12W of output power, will actually be well above comfortable listening levels on most speakers). You do need some 8Ω 100W load resistors to make that adjustment. It's not critical to do as long as you kept it at the factory value, in my experience.