Sheriff's suggestion was for the council to help us build the new stadium meaning our finances don't come into play at all.
We've had 5k+ this season easily without having any of these "specials" you've talked about. If you mean the offer last season when we played York (£5 a ticket) then we got over 9k in that game, in League 2.
In League 1, we were averaging 7,850 in 2008/09 (with a high of 10,240) and still managed an average of 7,718 in the 2009/10 relegation season (with a high of 10,329). In the Championship season, we averaged 10,024 - highest attendance being 11,415 and a low of 7,901.
Add to that a new stadium will in itself bring added interest and an extra "buzz", if we were to gain promotion to League 1 with a new stadium of just 10,000 then we wouldn't be able to hold the highest attendance from the last 2 seasons in League 1.
So while a 22k stadium is not needed NOW, it may be needed in the future. IMO, we should look to build a 14-16k seater stadium with the chance to increase.
That isn't the end of it though. What we should also try to do, which I believe is in the current plans, is allow improvements to the training ground to not only improve facilities for the first team but for the Academy as well. Ricky Duncan said recently in an article on the OS that we are one of the top Category 3 clubs and we are practically coaching at Category 2 standard. The only thing preventing us being a Category 2 standard club is the facilities and funding. The funding will hopefully come from the non-match day funding (as mentioned earlier and I will briefly go into below). If the council are willing to build the stadium, then we could persuade them to help with the facilities too - IIRC we need an indoor 3G pitch and they cost a couple of million too.
As for non-match day revenue, I'm not going to bother going into this too much as I've written enough as it is! We can all speculate and say doing X will generate £Y per season and doing blah will allow us to pay for blop. All we know is that the main stand has the potential to generate a decent amount of revenue. Just a quick look at this graph below (via Deloitte) shows that we could go follow how the Germans do it and have cheaper match day tickets - would certainly help us fill a 14k stadium in League 1 - but will need to boost Commercial (i.e. non-match day) revenue by quite a bit.