Is it alright to use a brass drop ear for my tub spout rough-in?

You defintely made the right call swapping that tub spout drop to brass instead of PEX. Using PEX for the spout is one of the most common DIY mistakes becuase the inner diameter of PEX fittings is significantly smaller than copper or brass. That restriction creates too much backpressure when the tub is filling, wich forces water up the shower riser and causes the showerhead to leak while you're trying to fill the bath. Since you went with a brass setup down there, you won't have that issue.

As for the showerhead riser, using blue PEX up there is perfectly fine. Unlike the spout, the showerhead isn't fighting a diverter gate, so the slight restriction from the PEX crimp rings doesn't matter. Just make sure you've got that drop ear elbow for the showerhead screwed into a solid 2x4 block. You don't want the shower arm wiggling every time you adjust the head. One thing to double-check is the **distance between the mixing valve and the tub spout**. Most manufacturers, especially Delta and Moen, have a specific rangeu2014usually between 8 and 18 inches. If you put the valve way too high above the spout, you can occasionally run into wierd pressure issues, but as long as you're within a reasonable distance and used a high-flow pipe like copper or brass for that down-leg, it usually works out fine.

Since you're still at the rough-in stage, give everything a good shake test. If you can move the spout or the shower riser by hand at all, add more blocking. Also, keep an eye out for any gray piping in the rest of the bathroom while the walls are open. That's Poly-B, and if you see it, you shold probably cut it out now. It's notorious for pinhole leaks and it's much cheaper to fix while the drywall is already down.

I didn't realize the distance between the valve and the spout mattered that much. My layout is a bit wierd and I was thinking of putting the handle way higher so I don't have to bend over to turn the water on. Is there a max height where the brass pipe stops being enugh to handle the backpressure?

On the showerhead side, is there any reason not to use red PEX for the riser if that's all I have left? I know you used blue, but does the color actualy change anything or is it just for keeping track of the lines? I'd hate to buy a whole new roll for a three-foot section.

You can use red PEX for the shower riser without any issues. The color is just a visual aid for installers; the pipe itself is exactly the same as the blue or white stuff.

Regarding the valve height, be careful about going too high. If you put that mixing valve at chest level while the spout stays at the tub rim, you're creating a long path of travel. Even with a brass drop, that extra vertical distance increases friction. If the resistance to the spout gets too high, the water will take the path of least resistance right up to the showerhead. Stick as close to that 12-15 inch range as your layout allows to avoid a constant drip from the top.