After a lot of testing, and with some things in mind, I've reached the conclusion that the best size is the maximum size for
official Futsal pitches - which is 42 x 25 - but rounded odd to 43 x 25 so the field has a "center" on both the Y and X axis.
Futsal is the official, FIFA recognized "hall football" or "indoor football" - and in many ways it is similar to football. It can (and is) be played outside on grass fields as well, so no biggie there.
So from what I've experienced, Futsal offers the best dimensions and team size (5 including goalkeeper) but the rules used can still be football rules, so you have some kind of generic mix of futsal and football.
Things taken into consideration for the choosing of this size were, mostly, the fact that larger fields, although interesting because of the speeds balls can achieve, are not as interesting since we can't play high (high balls, crossings, etc), use the head, etc... And Futsal is generally more "grounded", most balls are low passes, so it flows better than a huge field.
Another thing that weighed heavily was the fact that, IMO, the field should ideally fit the whole render screen both for players and the audience. A field too large will be stupid to watch as the audience won't be able to see the other side (for example), and it is better if the field and the audience can all fit the same rendered area, so everyone can enjoy the spectacle.
Those are the things being taken into consideration for the construction of Aurora's Arena, which shall probably be finished this week and ready to receive matches :3