I see 3 definite needs:
A goalkeeper - a new number 1 - we need to replace Howard for sure in the end of the season, I would think playes like Handanovic, Valdes or Mandanda could be decent options as their contracts in their clubs are ending and so could be cheaper to bring them in
A creative attacking midfielder that can play number of positions - ideally Yarmolenko - we need a long-term player with a big creativity to play in our offensive 4 with Lukaku, Barkley and Deulofeu, Yarmolenko would be absolutally ideal player for that position, he could also cover Barkley's playmaker position if he would get injured or out of form and so there would be no need to buy a backup for that position
A striker - I think Kone is decent backup if Lukaku gets injured, we still have Naismith and young Rodriguez fella but we really need a top backup for Rom if he injures himself - an option could be a player like Austin or Kokorin again with an ending contract
And another few maybes:
A right back backup - the question is if Mattioni can make it, I believe he will get a chance in the second half of the season, and I have some decent hope he could be a good option for a backup for a season or two till Kenny is good enough to play for the first team
A goalkeeper backup - firstly we have only Joel if Howard is injured, and I think only one player is too small cover during these days, and secondly I think Joel could do with a season on a loan when he would start all the games - the ideal scenario would be to buy a first keeper that would fight a season with Howard, bring in another backup for Joel and then when Howard goes out in 2017 then we have 2 new goalkeepers and Joel with a needed match experience back fighting after our number 1 position in the goal... but if Joel stays, then we don't need anyone, Joel is good enough as number 3 for sure
A central midfielder - as Barry is getting older and older, it would probably be a good idea to maybe prepare a potential backup for him and so buy a young player that GazBaz could teach some of his things and that may fight with Besic, Ledson or Cleverley to replace him when Barry goes
My only hope we still will be going the way to mainly go after cheap players/free contracts or young players that does not cost too much and then splash majority of our transfer budget on one or two players with a big potential (like McCarthy, Lukaku or Funes Mori) and give chances to young players from academy too. I love Roberto's way he dealt with transfers during his tenure here so far.