I wouldn't worry about smoke out of the exhaust, white smoke in cold weather is perfectly normal when cold.
What you say about the damaged ht(spark plug) leads might make it misfire, this will cause vibration, loss of performance and will kill the cat, just go to a recommended garage, sorry to say it but if worried take a man with you even if he has no clue about cars as they won't know that.
I don't think the situation is as bad as it once was though with regard to this.
tabetha