spark plugs and coil pack replacement

[danksl]

Hi i'm new to this site,I registered because I was hoping for some advice before I waste money. I have a focus 2002 model,it has a leak in the gasket cover which is messing up the cat, sp plugs and coil pack. I'm not bothered about the cat or leak at the minute,last week it started misfirng so  on monday i changed the spark plugs,all fine for  a cple days then yesterday it started misfiring again. So now i'm gonna get a coil pack and hope that sorts it for a while but what i need to know is even though it had new plugs on monday is it best to order new pugs too with the coil pack and change them again? 

this car has been great really,struggled on through its problems,a year ago it started misfiring so my mate changed the plugs and its been fine since it started up again last week,cant afford to take it in so hoping coil pack will sort it til september  . Any advice wouldbe much appreciated

 

Also should i be disconnecting the battery when replacing the ignition coil? I'm only just starting to do what bits i can on my own car so have no real mechanical knowledge