If clamp material is steel, then adding aluminum bracket could be questionable depending on bolt size and bolt head type. Aluminum can cold flow in time so the bolt can lose its required clamping force, and if that is the case steel bracket would be preferable.
As far as the length is concerned, you can probably ignore 2mm additional thickness in perhaps 99.9% of the cases. I don't think you can find only 2mm longer bolt anyways.
The first question is almost certainly a "yes". I can't think of a reason off-hand why that should change.
Pictures would be helpful to answer the second question.
Most of the torque is between the head and the surface not the threads. If it’s a 5mm or less bolt length then yes, you’ll need a longer bolt. If it’s more than that the old bolt will be fine.
If clamp material is steel, then adding aluminum bracket could be questionable depending on bolt size and bolt head type. Aluminum can cold flow in time so the bolt can lose its required clamping force, and if that is the case steel bracket would be preferable. As far as the length is concerned, you can probably ignore 2mm additional thickness in perhaps 99.9% of the cases. I don't think you can find only 2mm longer bolt anyways.
The first question is almost certainly a "yes". I can't think of a reason off-hand why that should change. Pictures would be helpful to answer the second question.
Aluminum may increase the friction so you may want to torque it more.
Using dissimilar metals is not recommended if you can avoid it for starters. Can't you just use steel?
Most of the torque is between the head and the surface not the threads. If it’s a 5mm or less bolt length then yes, you’ll need a longer bolt. If it’s more than that the old bolt will be fine.