Can you use a paintbrush to apply model glue for polystyrine models, and if so, what do you use to clean the paintbrush off?
Also, are there different or better glues for modeling?
Yes, you could use a paintbrush or simpler buy a glue that comes with brush in the cap like the Tamiya ones.
I use a variety of glues for modeling, each one has its application, good and bad points.
Plastic Cement/Glue (selection thereof)
White Glue
2-Part epoxy glue (different setting times)
Super-glue
etc
Some of those will work on a rnage of materials while others are specific.
Rather tha a brush, find a technical drafting pen which will allow much better control of placing liquid cements. If you must use a brush, get one with a pretty narrow point and use it only for glue. Acetone (finger nail polish remover) will clelan build up, but ultimately the brush will not last very long.