We're in probably the best position in about 15 years to attract talent at the moment, but squad size (and one eye on FFP) could prevent us from doing what we want to this Jan. Hopefully Unai sees bringing in a RB as essential and buying someone versatile, like Geertruida, would mean that multiple positions can be covered by one player. I get the feeling that for other positions though, we'll be following a one in, one out policy.
For example, if Olsen goes, we might sign a younger keeper like Josh Griffiths. If Digne goes, we might sign Acuna (though I'd prefer Barco). If Chambers goes, Ronnie Edwards. Dendoncker > Vermeeren. Traore > Summerville. Duran > Dybala etc.
Having too large a squad could disrupt harmony and mean certain players aren't registered (especially as we have to balance the Home Grown quota as well). We also don't want the squad to grow unwieldy, as it could impact FFP down the line, especially as Champions League qualification isn't guaranteed yet. For those reasons, I think it'll be a quieter transfer window than most of us would hope for, unless we manage to sell the players above. If it does end up being quiet though, I reckon the summer window will be a big one.