How do you determine how much lift you need for the wing...size of the diver...the tanks being used....sorry if am asking too much
You can never ask too much !
Well I am not an expert but I’d say, for cold water, if you take 30lbs for a single wing you are likely to be sorted and 40lbs is enough on doubles for most people. (I think you can get away with less lift for a single cylinder if you dive a warm area because you won’t wear a thick wetsuit)
The exact way you determine how much lift you need is complicated.
You need to know how much negative you’ll be at the worst point of the dive: the big unknown if you use a wetsuit is how much it will compress at depth. When a wetsuit compress it will lose buoyancy and that can be quite a big factor if you go deep. Also the air in a single cylinder will add roughly 2.5kg at the beginning of a dive.
This assumes that you are neutral at the end of the dive when your tank will be at the minimum pressure reserve you choose.
Also if you want to be strict you should plan for the loss of a wing, this means that if you are more than 5kg negative at some point you probably want a second source of buoyancy. This can be a lift bag, a DSMB or a drysuit.
Some other people here with more experience will chime in ...
Alternatively, find some people in your area who have the configuration you want and ask them questions or even to try their equipment if you know them well ?
EDIT: I bought my 40lbs single wing thinking that it cannot hurt to have 10 more lbs.
If I could change it, I’d prefer to have a 30lbs.
The 30lbs is slightly more streamlined so it’s a bit easier to dump and move the air to the valve by raising the lower left side.