Last week or so I have been trying to think through how I would approach the offseason and how we could better this squad for a run next season assuming minimal cash available. I started by wrestling with the idea of base formation as a means of determining how each group needed to be strengthened. I have no doubt in my mind that Emery wants to get back to his 4-2-3-1 roots. However, based on our best performances this season, I think we really need to stick with a 2 ST setup as our base with the option of going single ST based on situation. And based on the current roster makeup (keeping the budget in mind) I think we should stick with a 3 man back line for 1 more season and begin the 4 man back transition next summer as Kos/Sokratis move on. So I would stick with 3-4-1-2 / 3-4-3 option this season with a plan to transition to 4-2-3-1 / 4-2-2-2 next offseason.
GK
Leno is the starter.
Cech retiring.
Ospina likely headed to Napoli. If not he will be sold somewhere else.
Need a #2. Martinez has done well at Reading. I'd be inclined to give him a shot at #2 and maybe find a cheap young option to push him.
Find someone to push Leno next summer.
CB
Sokratis is probably our most solid defensive CB. He has some flaws but should be retained.
Kos is our best defensive leader and a tireless worker. Assuming he wants to stay he should retained with the intent of him being a backup before Jan.
Holding started the season really well. He should start the season as the #4 with the hope that he rebounds and takes Kos's spot in the starting lineup.
Nacho is getting older. I've seen reports that he is a FA and others that we kicked in an option to give us 1 more year. Either way I think he is gone.
Mustafi has his moments and does some things well but really shouldn't be making so many mistakes at this point in his career. Sell him for whatever you can get for him.
Mavropanos didn't get nearly enough playing time this season. Unless the coaches think he will push into a starting role next season I'd be inclined to loan him to a German or Championship squad where he has a good chance to play.
Chambers is a wild card. He is still fairly young. His only effective position in the backline is as a RCB in a 3 man setup. He also showed capable of playing a DM position on loan this season. I'm a little torn what to do with him. If a big enough offer came in I might be inclined to sell but I am kind of partial to the idea of giving him a season as a RCB/DM super sub and see if he can earn a roster spot moving forward.
With Nacho & Mustafi out you need a minimum of 1 CB. If you loan Mavro you need a 2nd.
For #1, I'd go with a starting caliber CB. I'd be fine with a vet (28-32) if he represents an upgrade and has some miles left on him. Thinking someone like Umtiti (likely pipe dream), Alderweireld, Gimenez, Boateng, Felipe (Porto) or Savic. Possibly Maguire, Keane, Glik, Bailly, Ake, Orban or Mandi.
For #2, I'd look for someone young and inexpensive with potential.
WB
Think you are mostly set with Kola, Bellerin & AMN.
Need a LWB that can atleast push Kola if not immediately take the starting job.
Wouldn't hurt to add a cheap RWB so AMN can have the flexibility to play other areas as well.
CM
Torreira is a given.
Duezy as well.
ElNeny barely played and should be sold
See Chambers note above. Think it could be worth keeping him around in ElNeny's spot to see if he can contribute.
Xhaka can be magic moving the ball forward but his defensive lapses and lack of pace are a huge part of our defensive issue. I'd be ok keeping him as a backup. Otherwise I'd sell to the highest bidder. Seen rumor that Inter is interested.
We are linked to Rabiot, Nkunku & Llorente. I'd honestly like to grab 2 of them if we can. All would bring something to our CM spot that is currently lacking.
CAM
Really don't think Ozil is going anywhere. We are stuck with his salary.
Think you need to start grooming someone to take his spot. Would love Fornals but I'm not sure there money is gonna be there with the other spots that need filled. Best bet is probably Iwobi or another W/AM type that can play multiple positions.
W
Iwobi should stay. If we have the money for a W overhaul I might be inclined to loan him out for increased games but as it is we need him to grow while he plays for us. Would be inclined to try him at AM when we are in the 3-4-1-2 base.
Miki is slipping and is not really a true W. Think he needs to be sold.
Nelson & Smith-Rowe return. Leipzig want to keep Smith-Rowe and I think we should allow it. Nelson should be given playing time on the wing when we go 3-4-3.
With a base 3-4-1-2 I don't think you need wings a ton but I think would still need to add someone with speed for situational play. My inclination would be to add someone that can play W in a 3-4-3 and ST in a 3-4-1-2 so as to improve our ST rotation as well. I'm thinking Zaha, Thauvin, Rodrigo, Lozano, Neres, Pepe (likely too pricey), Bergwijn, Correa, Rebic, Chiesa or Pavon
ST
PAE & Laca rumored to be extended.
Nketiah did well when he got to play but really needs a loan
Could solve some ST depth with my W suggestion above but it may also not hurt to find another inexpensive option.
Recap
Starting - CB, CM
Likely starting - LWB
Depth - W, ST, CB