I am in my first season at Chelsea and who should I buy with my 14 Million, and who should I sell?
Either try to sell or loan players who you feel you need to move on to improve the squad, then use the money from their tranfers/freed up contract space to give yourself more money to buy players with.
As villadam said, if you can get Subotic for 12.25mil pounds (about 20-something million US), then he'd be a quality pickup for you.
If you need cheaper players though, I highly recommend Alvaro Dominguez from Athletico Madrid, I got him for $13.75mil US and he's been a solid first-teamer for my Arsenal squad.
Andre Ayew for $18mil US is one who I consider a great pickup, although his net-worth decreases to around 10mil after a year, his stats and play more than make up for it. His brother Jordan can be picked up for around $11mil US as well, although he'll need to be given extensive first-team or loan experience to realize his potential (since you have Lukaku you may as well not sign him I suppose).
If you need English players for Homegrown status purposes, Fabian Delph is a solid pickup for the midfield at $11million US from Aston Villa. Ryan Shawcross should he tagged for later transfer as he's fairly well-rounded and tall (6'5").
Yaya Sanogo can be bought for relatively cheap if you want a striker you can develop along with Lukaku (he's tall, 6'4", with solid physical attributes). Carlos Fierro as well but you should wait for a year or so to see if his price drops or you have enough money to get him.
Keep a close eye on Man City too as they have players who will seek to leave as they keep buying the rest of football to win something. Most obvious is Tevez, but he's a huge gamble as he's a drama-queen.
Also, scout Lornezo Cristeg from Inter, he's on a youth contract and has good enough potential to warrent a look-see on your reserves squad.