Suggestion: additional group management functionality

Suggestion 1: add to group.
When pressing for example, Control+Shift+1, I would like the currently selected units to be added to group 1.
Motivation: makes it easier to manage groups that have refinforcement arriving.

Suggestion 2: select ungrouped units.
When dragging the mouse with some currently unused modifier key held down, I would like only ungrouped units to be selected. Alternatively, there could be a hotkey that simply deselects any selected units that already belong to a group.
Motivation: I tend to have "parking lots" where factory output is shoveled to before they are assigned more meaningful orders. At the same time, the parking lot could be travelled through by other units on patrol, which means if I drag-select a bunch of units, I will also include the units who are doing other jobs, not just the ones parked. If the patrolling units are assigned to a group (easy to do when assigning orders thanks to suggestion 1) and then I can avoid selecting them and "stealing" them from their current job.

An easy way to add units to a group is to press say.. group one.. So now you have the group highlighted, then shift select any units you'd like to add to that group and press cntrl+1 so they all get added.

That.. Should work, I think.

that only helps with problem 1...

i rarely use groups, but i understand your problem and am all for advanced seletion filters

Suggestion 3: expand selection to groups.
When I have some units selected, I want to be able to press a button and select the groups these units belong to.
Motivation: I might not remember the right group number but if I have a part of the group on screen, I can just click on one unit and expand to have the entire group selected with low effort.

Suggestion 4: non-numbered groups.
I want to be able to group the selected units into a unique group that cannot be recalled via a number, only via the "expand selection to groups" feature. This could be used any number of times, each time creating a new unique group. For simplicity of implementation and UX, each unit can only belong to one non-numbered group.
Motivation: I like having "construction gangs" around - a bunch of fabbers, with possibly some defense. Having to group these into number groups can make me fast run out of number groups. Having non-numbered groups means I just need to select one member of the gang, hit the "expand selection to groups" button and I have selected the gang without any fuss.

Some kind of visual cue would be in order, though, I think. Such as assigning a name to each such group when creating it. This name could then be displayed on all members when selecting one. Plus, add a list of all such groups for quick reference somewhere as part of the UI.

For 1:
Hit 1. Bring reinforcements into view. Ctrl+Z. Ctrl+1
Only minor issue is that on QWERTZ keyboards Z is right next to U, so I keep disabling my UI by accident.
While it is limited to units of the same type it is rarely that a group has lost all units of one type already.
Personally I would prefer it if I could order Factories/Teleporters to just add units to the group as I could in SupCom.

For 2:
There are only so many modifier keys. excluding Fn (Laptops only), we have Ctrl, Shift, Alt, Maybe AltGr. You cannot combine them freely and you really have to rationalise them carefully.

For 3:
If this is only about expanding the current system just showing the group numbers in the selection border should help. That way you figure out the number after selecting the first.

For 4:
Is tied to 3.
Technically there should be no limit to the Nr. of groups. But command groups primary purpose is to have a group quickly selectable via a number key, even when offscreen.