Multi-Drive Migration from old MacMini to New Unit w/Migration Assistant Questions

I currently own and use a MacMini (Late 2012 / i5 Dual-Core / 16GB) running Catalina (10.15.7) with the following storage:

• 250GB Internal SSD (30% free) - System & Apps
• 500GB Internal SATA Drive (35% free) - User Data/Files
• 2TB External USB Drive - User Data/Files

Though running fine and has served our family well, it’s past due for retirement as our main unit having reached both O/S and some application usage limitations (ex., Quicken, VMWare) due to age.  I am in the process of planning a move to a new M2 chip configured MacMini and have been researching the use of Apple’s Migration Assistant (MA) to migrate my system and user files.  I’m hoping to purchase the 256GB / 8GB memory or possibly the 512GB / 8GB memory configuration.  My current plan was to migrate using the MA application at least for the main SSD drive to safely move user and application data, and simply copy the 500GB SATA drive folders/files to a new drive with a USB or Thunderbolt interface, and plug into the new MacMini.

Question(s): 

1. Would the Migration Assistant app allow not only the migration from my current 256GB SSD to the new unit’s 256GB SSD drive, but also separately manage the movement from my 500GB SATA drive to another external drive? Or is the app only targeting system/user files on the main drive?   Most of the documentation I’ve read so far seems to imply it’s a single movement procedure of all chosen files, but I will need to do this in phases and haven’t found this documented or in any other Community entries so far. 
2. Is an external USB the right choice for the 500GB files new home, or has anyone found a more efficient interface? I’m leaning towards the Crucial X9 1TB Portable SSD as my replacement for the 500GB drive, the Crucial being USB-C and thinking I may not need the addl native Thunderbolt transfer speeds based on my limited application usage so I wouldn’t need a new separate enclosure and disk.

Thanks, and looking forward to any comments or suggestions.