This
thread by Cleon is from a couple FM's ago but the ideas almost all hold up. Quite honestly a couple his treads (as well as Rashidi and Ozil-to-the-Arsenal) would make for some informative reading. Personally, I wouldn't marry myself to a particular formation or any specific player roles until the club is decided on. The reality is that a possession tactic can be created with almost any shape any with any level of fluidity.
The key with any possession tactic is going to be movement and options. You need to have players moving, creating those constant triangles. A lower tempo tends to connect to ball retention. You don't have to press, but if you are valuing the ball, it makes sense to try to get it back ASAP. I prefer to press via Team Instructions but OI works too. Using OIs for pressing can be impact the defensive team shape a bit more, it seems.
Picking the side is a key part of it IMO. You want fairly technical players for the level. I would be looking for Technique, Off the Ball, Composure, and Decisions. Passing would be a nice bonus but less necessary than one might expect. For the pressing, you would want Stamina, Aggression, Teamwork, and Workrate. A couple of players with Vision and Flair will help it from being dour. What club depends on where your interests lay, as there are tons of options that could fit. Loads of German, Spanish, and Italian clubs have those kind of players. Some in The Netherlands and Portugal. I would probably say try one of the big three in Portugal, Ajax in The Netherlands, or a mid-level German club. Now once you have picked a club, then you can look at the talent you have and select a formation that suits the talent. That's not absolutely required - you can play players out of position quite successfully. But its a logical approach.
I've done pretty well with possession tactic with formations like 4-1-4-1 and 4-2-3-1 deep-deep. The key is always having options available. This will come down to the roles & duties you choose and the players you have as much as the formation itself. I would actually avoid using any Team Instructions, except for maybe the Pressing, until you see how it plays. You need to watch matches and tweak to have it work most effectively. Shorter passing, while it seems logical, may be detrimental at times as it can unduly restrict options. A high line can be very effective, but can also reduce the effectiveness of attacks as the opposition is compressed and you are left with no space to exploit. Watch for issues like aimless passing between defenders and deep midfielders - can happen with lack of options if more advanced players are out of passing range.