Cats periodically do vomit. Mine does if she's eaten too much or too quickly. Or just if she feels like it really! lol As long as it's just a one off and he's eating and drinking and is active he should be ok. If he keeps vomiting then take him to the vets.
With all the problems you've had recently I'm not surprised you're worried about him. Try to take some deep breaths! lol
