In January, biggest issue regarding buying players isn't going to be money - its going to be how many slots in the squad are available to fill.
In terms of overseas trained players we have the maximum of 17 (under UEFA definitions), so to sign any overseas trained players we will need to sell.
There are rumours of a deal for Wanyama to go to Hertha Berlin which would create one slot.
Of the 3 amigos whose contracts run out at end of June 2020, it looks to me as if Alderweireld and Vertonghen are playing both well and regularly. In short I don't see either leaving in January - and its up in the air to me whether a contract extension for one or both will be announced in the next month or two or one or both will leave in June.
The 3rd amigo, Eriksen, is playing well enough when coming off the bench (Wolves being a good example) but imo he is more likely (not a certainty) to move on in January.
Whilst I think the club would listen to offers for Rose, it sounds more likely he wants to be stubborn and see his contract out, and whilst I'd be happy to see Aurier, its only if we brought in a decent RB option in January too - and co-ordinating that isnt going to be easy. No other obvious candidates to leave that I can think of.
No problems on the Home Grown front, we have 2 spare slots. However the much bigger problem is identifying and buying suitable players to fill them, the list of candidates is really not that long.
So best case Transfer Window :
1. Wanyama and possibly Eriksen leaving allowing us to buy one or maximum two overseas trained players (three at a stretch if we can sell Aurier and buy a RB).
2. Up to two HG players bought to fill available slots.
Worst case is of course no Overseas Trained players leave so we cant buy any either - and no HG players arrive !
Reason to be optimistic of some movement in January is that this summer if not going to be that easy to make transfers as most European players will be involved in Euros, which with a 2 week training camp before hand and three weeks leave for players afterwards......occupies most of the summer from mid June to start of PL (so almost no pre-season for players again).