Which hammer drill should I buy

First of all, I have to say that with the volume of work you have you can just mix the thinset by hand. I once had to install about 2.7 square meters of tiling and mixed several small batches of thinset with a spattle - no problems at all, I wasted much more time on applying the thinset and installing the tiles evenly. Totally not worth risking the drill.

Next, you should not use any drill for mixing unless its manual says it's suitable for mixing or that it has overload protection that slows the drill down in case of overload. Drills explicitly suitable for mixing are typically professional drills with very low RPM (500-700 RPM) and so very high torque. The "HF corded drill" you reference is nothing near that. Drills with overload protection are typically professional cordless drills with smart electronics that monitors all the parts for overheating and reduces the output power in case of overload. The Milwaukee M12 you have likely has the right type of overload protection (that's the impression I have from reading the online specs of the drill) and so you likely could use it for this purpose.

I think you're on the right track, especially in considering TWO saws, one high-speed saw dedicated to wood and another very different low-speed saw for brass/steel. The wood saw will be fine (but messy) with alumin(i)um.

You should know a couple more more points.

First, the kerf on nearly all bandsaws (except sawmill types) is pretty much identical regardless of blade choice.

Second, a saw with a gearbox (don't DO this with a variable-speed motor!) for two very, very different speeds (wood and alumin(i)um require MUCH higher speed than steel will tolerate) will tend to be a very high-ticket item, generally much more expensive than two dedicated saws because of the dramatic shiftable gear reduction required for steel.

Now... to really answer your question of must-haves, we should know what - in particular - you plan to cut, and how accurately you want to cut it. What thicknesses of wood and metals? Do you ever plan to cut steel or brass (if not, you could do with one saw)? Do you require high-quality cuts in non-alumin(i)um metals... or could you do that work with a reciprocating saw? In wood, what are your goals? How large (length / breadth) a workpiece do you really plan to cut curves in?

For most steel I imagine you cutting, A small (4") vertical or vertical-horizontal bandsaw would suffice. I have one such from Harbor Freight in my shop, and it does everything I want a steel-sawing saw to do (which is really quite a lot).

A 14" bandsaw is the de facto standard for a "serious" woodworking shop. A wide array of manufacturers offer them, they all take one common blade size (unless they have a "riser" to lift the upper wheel another 6", in which case they all take a second common blade size).

You should know... that most bandsaws have a considerably smaller vertical capacity than the saw's "inch" size (which is a diametric measurement of the upper and lower wheels). Most saws have about a 6" vertical capacity, and that's really pretty realistic unless the saw is equipped with a very large motor; cutting material more than 6" thick requires a GREAT deal of power. A riser will gain more height capacity, but it's nearly always wasted capacity because the motor can't manage resawing stock that's much more than 6" thick (unless it happens to be balsa or basswood or tupelo or other very soft wood).

I like the 14" saws; they're generally built much sturdier than smaller saws, and have better blade guides. Blades are easy to come by. The basic saw, with no "upgrades" (some of which are glitz with no real practical upgrade value at all), works well for most tasks. Because they're so very common, there's lots of help available on the Internet if you should run into trouble aligning, maintaining, or using the saw.

I apologize in advance - I'm afraid I've rambled a bit here...