I'd guess Eco Communities may also tender, have you thought about the consortium working in partnership on a joint bid? As they already run community libraries in the borough and have a "proven track record" in doing so, partnering with them will put you in a much stronger position to run the library in the way you would like and in a manner that will generate sufficient income.

How will the income be generated? Consider groups that may be interested in using the available meeting space? or out of hours events such as film nights?, for corporate events? Local interest group usage? Scouts & Guides meetups, After School events, specific school events, author book launches and signings? Setting up a Friends of Forest Hill Library Group if it does not already exist.

Has the consortium put together any type of business plan to determine how much income is actually needed to run the library as a not for profit organisation so all revenue is ploughed back into its operation?

Personally I think you'll need it to run as a profit generating enterprise to be able as an example to cover the maintenance and repair costs bearing in mind the age of the building, heating and lighting costs, (which the council should be able to give you an idea of the annual expenditure), a copy of the accounts for the library for say the last three years so you can see the current expenditures, Replacement and purchase of new books, maybe foreign language books and films, hiring out dvd's and blu ray films, mechanism to chase up overdue returns, all this will eat into any revenue that is generated.