Using Aski's example .....
So if we got promoted, & say, our turnover was only £30m in the Championship, does that mean that Manc et al are only able to spend 70% (or 85%) of £150m? Or does the guaranteed £89m get added to our £30m before the anchor is applied? (i.e. 70 or 85% of £119 x5 = £595).
And how do we determine turnover if the financials are published after the season starts?
No WJ, City would be allowed to spend £503m ( based on 70% of their turnover of £718m). The spending limit is either 70% (or 85%) of a clubs turnover or the agreed "anchor limit" for that season, whichever is the lower.
I would expect the "anchor limit" to be set based upon turnover + central fund payment, so in your example this would be set at £595m (being £119m x5) Thus any clubs that had turnover exceeding £850m (850m x 70 % = 595m) or £700m ( 700m x 85% = £595m) would be restricted by the "anchor limit" (again this presumes a x5 multiplier. A x4 multiplier would set the "anchor limit" to £476m and thus City on this occasion would be restricted to that figure instead of the PSR figure of £503m)
The reason the Central Fund payment is included is if we decided to form WJ-Aski United and somehow immediately got promoted to the Premier League despite never having played a game, we would receive our share of the central fund and that would be our proposed turnover for the season, even before we sold tickets to the games and got sponsored by Wakey's Whippets as we played at the newly constructed Ellandback Park Stadium.
The problem with trying to work out the exact details is that most explanations are a summary and thus don't go into the precise details. Because it's only a trial at present the F A haven't published full documentation so your questions may not be answerable until nearer the end of the season. Until then all we can do is guess, based on information from factual sources and opinion. Also the documentation on the UEFA site is over 600 pages, and contains far too many words and not enough meaningful numbers
WARNING - The following contains numbers and maths and is also just an opinion 
As for determining turnover for the forthcoming season, I'm presuming it will be very similar to what clubs already do, in that they will be submitting financial forecasts, prior to the season starting and then also on a regular basis.
Possibly the FA may say if your forecast for turnover is only 10% greater than the previous season, then its automatically approved, anything more than that will need to be clarified and individually approved.
Luton's forecast might say that they expect their turnover to increase by 50% from £18m to £27m due to promotion before payment of the central fund, and the FA may find that an acceptable forecast.
Another of the promoted clubs may say well we were in the EPL 2 seasons ago and got relegated, so we are basing our forecast on those figures, and again the FA may find that acceptable
Newcastle may say they expect their turnover to increase from £250m to £750m, to which the FA responds that their turnover forecast is set at £275m until the club provides factual evidence for the substantial increase. Maybe they have just qualified for the Champions League, gained new club sponsors and sold the naming rights to St James Park as well as sold or are in the process of selling a number of players which makes the forecast legitimate. Alternatively the FA may not be convinced that Ahab The 2nd Hand Camel Seller really paid £500m to be the new shirt sponsor
Obviously the above is a simplified opinion which no doubts has many flaws, and its virtually guaranteed that the F A will have some sort of system that no one will ever understand
