There are elevators in the building and I am pretty sure the city made all buildings become ADA compliant. Enjoy!

I kind of doubt it. But you could call teh Destination Detroit tours. They would know.

You can get into the former banking chamber at any time during normal business hours, but the tour is run by docents from Pure Detroit which has a shop there. The tour is free but the docents are worth a top - and some of the stuff in the shop may entice you too. The tour takes you to parts of the building you could not otherwise access with a lot of explanatory information which puts a context to the whole thing.

There is often ample street parking available pretty much all over the city, but be careful to watch for the meters. They are skinny units and not very tall and there may be only 1 in a middle of a block. Bikes are sometimes tied up to them which makes them even harder to spot. There is zero tolerance for not seeing them even if you're an out-of-towner and the ticket costs $65! You put in your credit card and plate # and pay $1-2 for 2 hrs. max. Kind of a pain if you want to spend any kind of time somewhere like the Guardian, DIA, Fisher Bldg.(a MUST see!), etc.

No there are 3 tours a day on the weekends. However, if there is a wedding or function the last one is usually cancelled.

You can also visit the building on your own, when it's open.

Depending on the area that you are photographing, you will not likely be bothered by anyone for bringing a tripod. The mural in the "Cathedral of Commerce" is well-photographed from the public space. The Bank of America financial center in the main hall has a security guard, but he does not typically interfere with people photographing the public areas of the building. The main lobby off of Griswold likewise has a security desk, but also much less space to set up a tripod; the main lobby is also the access point to many of the Wayne County offices, so that could create some access or traffic issues. You can always check at the desk to see if there are any restrictions that may need to be followed.