I got used to not having group-select when I played it a few months ago. The game’s simple enough not to require as many units as C&C does, and I found the number of units required to complete the missions was usually manageable, provided you make liberal use of the vehicles ability to squash dudes. I was playing as Atreides, though, and they’re supposedly the easiest house.
I found the minimap that appears once you build an Outpost to be essential because you can click on it to give orders without having to pan away from your current view. Click a unit, press M for move or A for attack, then click somewhere in the minimap to complete the order. This is especially nice for quickly ordering those blundering harvesters around.
I remember completing this game as a kid, only to see various parts of the emperor turn purple before my weird knock-off copy hard locked after the final battle. I think I played Ordos then, I remember their ability to take over enemy units being stupidly overpowered.