Did I buy spark plug leads for no reason? And why oily plugs?

In my eagerness to continue my newbie mechanic adventures with my 2000 CE, I bought new spark pug leads to go with the new spark plugs. I was confused as to why I have four plugs, but the box of new leads contained just two. I've since realised that I did indeed only fit two leads, because I didn't buy new ignition coils (right?) which are WAY more expensive. So, even though this isn't a bad thing, have I made a bit of an error in buying just the two leads which obviously connect to only two plugs, with the other two plugs still running off the old coils? (Can't afford new coils, not yet anyway).

Also, when I fitted the new plugs, the old plugs had an amount of oil around them. Not lots, but a good coating. I figure this isn't right. If my research is right, I think I need to buy and fit a new valve cover gasket and seals? Is this correct? I hope so because the replacement is only about $60 and the job looks within my capabilities.

Cheers

The 4g93 runs an ignition system known as wasted spark. Essentially one ignition coil powers two cylinders, as the coil will fire off a spark every stroke according to signal from the ECU (meaning one spark event is correct, and the other will spark during the exhaust stroke). Its a highly efficient method for efficiency and emissions.
The 4g15 runs a single ignition coil that powers all four cylinders, based off the distributor.

Oil in the spark plug tubes is usually worn out or dried spark plug tube seals. These can be found for a few dollars each, and to replace take off the valve cover and just yank up the black tube seals. If you take the cover off youll see exactly what im talking about.