you need to know field size estimated from seismic
then u can check surrounded reservoirs similar with yours for porosity, water saturation, permeability, volume factors and so on.
for contacts you can also came with a range
finally you could provide a range for in place volumes

then depending on reservoir type you could plan a developing strategy.
no of wells depend on reservoir size and properties
same size reservoir with worst properties require more wells or/and longer trajectories or/and more sophisticated completions, treatments before starting into production
then you have to decide , depend on data u have, if u need pressure support or not
after that you need to choose a recovery factor based on statistics, empirical formulas, this will give u a cumulative
at the end you will came up with production profiles, plateau production and decline, that will fit into already calculated cumulative production
don't forget to assume a number of wells as unsuccessful wells, wells that won't have production. this is allways happening when you are developing a field