Yup, that can definitely be a hurdle! 
I’ve not used Blender really, so I’m not sure how to get UVs from it. I did find this image from Blender 2.66a that may still be relatively similar.
Using the textures from Quixel through Photoshop is no different than making a texture to apply in Gimp. The only difference is how Quixel makes it. It will export from Photoshop the same. It will save as the image type you specify and then in UE4 you can apply those textures to a Material that you can modify further. 
As for tablets. I’ve got an Wacom Intuos4 at home. I got a decent deal on Ebay for a used one. It take a bit of time using a tablet and looking at your screen rather than where you’re hand is drawing. It’s well worth it with the DPI settings of sensitivity and getting a good look and feel on your textures!
Good luck and if you have any other questions feel free to post on the forums or here on the AnswerHub!
Tim