Great post, refreshing to see.
I do believe there will be quite abit of activity in the market, with aquisitions and sales. I think the positions we should be looking at are LB, RB, CM, AM.
LB - This is an area which needs reinforcements imo, Evra has declined in the past few seasons with his defending becoming non existent at times. We have some very talented full backs in our ranks with Fryers, Blackett, Giverin, these all have great potential to become our permanent full back in the next few years, I have high hopes for Fryers. Fabio looks set set to go out on loan probably abroad which for me is odd if his future is in the PL, Fryers looks set to go out on loan also leaving us with Evra as our only LB. For this reason I believe we will sign someone in this area, I think someone around 25-28 age range to give a good 3-4 years and allow the younger players to develop ideally Baines.
RB - This positions has been constantly tried an tested yet we only have one natural RB being Rafael, who has his own problems. Smalling and Jones' future is at CB they should both be plying there trade in this area to help them develop, so some competition is needed in this area with Clyne looking a good prospect.
CM - This position is a must imo, I certainly feel that this will be filled in one way or another. At the minute we only have Carrick on a consistent basis, Cleverley has a bright future, Scholes and Giggs aren't getting any younger, Anderson cannot really be relied upon plus he could be sold, Park again could be sold, Fletcher has his illness which isn't going to go away so again we cannot rely on him to be fit and finally Pogba we still do not know how that situation will unfold. In my opinion we need someone more defensive but a box to box midfielder around 21-23 age range to develop alongside the likes of Cleverley so someone like Strootman who has great potential could be an option. On the other hand we could go for a more creative sided CM like Modric although I don't think we will pay his price and could look at a cheaper option in the mould of someone like Cabaye.
AM - With Owen leaving and Berba shortly following we look set to invest in this area in Kagawa/Hazard type player, who would provide cover for Rooney also be used in other positions and could see a slight change in our formation and style of play.
There will be departures with James, Da Laet, Owen already gone I think players like Berba, Bebe, Kuz, Park and Anderson (possibly) soon to follow.
As for your suggestions, Allen looks a brilliant talent and would easily slot into our system, he has great potential and with players building around him he could flourish another player that has flourished with Swansea is Glyfi Sigurdsson currently at Hoffenheim, who is a more goal scoring and creative sided cm. Both would be fairly cheap and are known fans so could be easy to tempt. Clyne I agree with, as for Hoilett he is very talented player no doubt but we don't really need a winger especially not a right footed one and he might struggle to break through where he deserves first team starts.