You don’t necessarily need 2 different UV channels.
Might be cleaner that way, but normally you’d only need them if you want to apply 2 different UV sets to the same faces. Also it’s only then that you need to move/scale your unused UVs out of the way, using 1 channel and Mat IDs would destroy UVs already set up that way (unless you move them over exactly one tiling UV square. Sorry about that - brainfart.
Also switching UV channels in the same Unwrap UV modifier means you lose the UVs of the channel you just worked on (unless you copy them over to the next channel, but the old channel will be reset). Unwrap UV works only on the active channel. If you want to have two channels active, you’ll need two Unwrap UV modifiers or collapse the modifier into your base object before you proceed.
For filtering (and I guess rendering) only one Mat ID in the UV Editor you have display options in the lower right corner of the editor window.
And for assigning different maps to different Mat IDs use a Multi Sub Mat like electrotoast wrote.
So basically you would assign your Mat IDs, filter them in the UV Editor to arrange them and a Multi Sub Mat to assign your respective maps. (Or a Multi Tile Map where you need neither Channels nor Mat IDs)