Looking to setup a 100Amp panel in my attached garage and have ideas/questions
The type of cable you linked to is SE cable covered by Article 338 of the National Electrical Code. It connot be used underground with or without a raceway. Here is the pertinent code language.

338.12 Uses Not Permitted.
(A) Service-Entrance Cable. Service-entrance cable (SE) shall not be used under the following conditions or in the following locations:
(1) Where subject to physical damage unless protected in accordance with 230.50(B)
(2) Underground with or without a raceway

Notice item 2.
You could use several other types of insulation in a raceway, including THHN, XHHW, XHHW-2. USE is for direct burial and can be used without a raceway except where exposed to damage so you need to sleeve it in PVC or metal raceway above ground.
Aluminum also needs an anti-oxidation compound such as NOALOX or ALNOX, there are many brands.
Rigid or IMC conduit can be buried only 6&quot; deep. Table 300.5
SE cable can be used as a feeder for interior wiring so if you kept the feeder inside the house and garage without going outside you could just protect it with PVC in the garage and be good. Or you could run the cable outside just not underground.
You will need a single 100 amp 2 pole breaker to feed the sub panel. 2 -50 amp breakers is not acceptable by the Code.
A separate disconnect is not required. The panel in the garage is not a motor so the &quot;within-sight rule does not apply&quot;. The breaker in the main panel can act as a disconnect. You actually don't even need a main breaker in the panel if you don't want one. You can buy a Main Lug Only panel if you wish. The main only panel you linked will do just fine without a main.
Good luck and stay safe!