Hmm, Coils and Plugs !
If the coils are ok, dont replace them,
As there is a lot of Chinese inferior coils out there, especially on ebay,
And when you contact the seller, they are reluctant to refund,
in a nut shell, if the coils are the OEM ones, only replace them in you need too.
i did just that, purchased a set of A/M coils, had a random miss on various cyl's, refitted the original ones,
Never had a issue for the last 43,000 k/m.
As for plugs,
again, playing Russian Roulette with the sellers,
I also bought plugs, and was very lucky I didn't have any issues,
You can buy decent one's off Ebay,
but buy from a reputable supplier.
If you can afford it, buy Iridium Spark Plugs,
they are more efficient and can last up to 100,000 k/m.
If you don't buy the coils, maybe put some of the money towards decent plugs, it will save you in the long run.
Average cost for decent Iridium spark plugs is around $70 > $120.