I don't know if it's a virus or sun damage. I get the same marking on some of my Cyms. leaves and I just cut it off. I find the new growth will come in fine with no problems. That's why I tend to think it's sun damage. Then again maybe mine are virused. Still they are growing and flowering.
The 2nd pic. of the leaf tip damage is definitely sun or over fertilization. I would just cut off and remove the damaged area. I do it for looks than anything else. I fertilize every 3 weeks and sometimes monthly. I also use a time release fertilizer that I sprinkle on top of the medium during the growing season. That way you do not need to fertilize every watering.
You might want to keep it separated from other plants until new growth comes in and see if the same problem develops. Also move it into direct morning sun gradually.
Did you have the plant indoors and then just moved it outside? That could be the problem. It's not use to the direct sun yet.
The pot is fine as long as the roots fit and there's room for new roots to grow. They can tolerate being pot bound really well so I wouldn't worry about the pot being too small.
Hope this helps. I grow a lot of Cyms. but I certainly am no expert. I hope it's not a viral infection cause that'll mean some of mine are virused too.
