If I understand correctly, you want to pull two home runs in 1 cable to a powder room, 1 for lighting and 1 for receptacles, yes?
If so yes you can but avoid the stacked switch and go with a two gang box if possible, you will need this for box fill. Cable to switch box is 3 wire, run your switch legs and run a jumper from the 2 gang to your gfi.
Take the red from the 3 wire and splice it to the black going to your gfi. All of your whites go together and your black from 3 wire feeds the switches.
Take a wire from the gfi and go to the other plug you have in your picture, this wire will go to your load side of your gfi. The wire coming from the home run is your line side. DO not connect your neutrals together here, they each go to their respective screw terminals.
In your panel you have to put them next to each other and either put it on a 2 pole 20 amp breaker, or 2 single pole breakers with a handle tie, so you can shut both circuits off at the same time with one movement of the hand.
Hope this helps.
FYI for original question, I would just stack the grounds but if you want to get a new bar then get one that matches the manufacturer of your panel, it will fit into a prep unchecked set of holes in your panel and comes with screws that will self thread into the panel back, no paint scraping or jumper from bar to bar required. This bar is only for grounds though.