Lag? i haven't heard of mods causing lag, at least not mine.
Crashes? Depends, but if there's an error caused by the mods i usually fix it.
Now, it's worth keeping in mind that the unmodded game can be laggy and can also be prone to crashes at times, so it's no surprise that you encountered these circumstances.
But since we're on the topic, what is the F&H that you modded and what are the mods that you are currently using?
What is the crash that you encountered?
This way i could possibly determine what's going on.
Also i'm glad that you found the mods useful, cheers!