The first thing I would do is scrap 4-2-3-1. In my opinion that formation, as with most of the most popular formations at any given time, work best for teams trying to maintain their position, and for top class teams with top class players. If two 4-2-3-1 teams meet, in the long run the bigger team will come out on top. We have to face the fact that we are the sixth biggest team in England, in terms of budgets. To compete we have to be daring, adventurous, inventive. We can't copy the bigger teams and hope to beat them while playing like they do.
To me, 4-2-3-1 has negatives. It has worked well for us against weaker teams, but against strong opposition we got crushed. The formation requires excellent individual and collective defending, and last season proved we lack both.
We also had problems with our midfield. If we tried to dominate games, we couldn't give proper striker support and lacked creativity, while we were too open in midfield when we tried a more offensive approach.
With an offensive 3-4-3 approach, I believe our individual defensive issues would be harder to exploit, and we would not start our games against the top teams in a negative way - like when Sherwood picked Sigurdsson as a winger against City because he was supposed to be a good defender.
In my opinion, if the opponent has a right back that is good offensively, you Don't put a defensively decent winger to defend against him, you use an offensively good winger against him and force their back to defend, so he can't use his offensive abilities.
I think a 3-4-3 would make our contra defenders look better. Vertonghen could get a free'ish role, where he could use his football brain and his abilities on the ball more than as a 4-2-3-1 central defender. Kaboul and Chiriches are mobile defenders who would fit into roles as RCB and LCB, and from what I've read that would fit Davies too. I also think Walker could do a good job as RCB for games where pace is needed back there. A three man central defence would also be more 'forgiving' in terms of including youngsters (Veljkovic,..) or players from other positions (Davies, Walker, and we remember the disasters that were Sandro and Capoue CB last season). Hell, I'm sure even Captain Daws could do decently. 3 centre backs would fit our squad a lot better than 2 with 2 side backs.
One of our biggest squad issues are wingers and backs. A side back need to be good crossers, good offensively and good defensively. Ours are decent, imo, but all are lacking certain important traits. Our wingers are worse. I feel that with our current squad, Lennon and Rose would be a lot better as right and left midfielders/defensive wingers/wing backs than they are in their current roles. Rose is ok offensively and has great energy, work rate, pace and acceleration, but lacks defensive awareness and positioning. Lennon took huge steps defensively last season, but has at the same time become less of a threat offensively. Both would be excellent wing backs.
The central midfielders would not have to carry as much responsibility. The defence behind them should be more solid, and the offensive trio ahead of them would do the creative work. That would allow for different configurations, a Paulinho when you want a runner to support offensively by coming into the box, a Bentaleb when you want a passer who can do a decent defensive job, next to a Capoue, Sandro or Dembele as ball winning midfielder.
Offensively we've had problems getting proper support for our striker, who will need it. Our three front men shouldn't have that problem. Holtby, Eriksen, Lamela, Soldado, Chadli could all do a great support job with less defensive responsibility than they have as wide men in 4-2-3-1. Different combinations of the afformentioned would provide us with possible variations in our play. Kane, Adebayor and Soldado would all look better as front men with better support and a more offensive team behind them.
I think a 3-4-3 would get us better football, make our footballers look and perform better, and bring better results.
From what I've read Poch is inspired by Bielsa. Bielsa often played 3-4-3. Poch should try that with this Spurs team, and reap the rewards.
