I think this is doable with a little outside of the box approach. Good suggestions so far so I won't repeat them.

Focus on timing. It is not an all or none approach with feeding or tilapia. In short I would feed in late winter early spring to get the BG up to their best condition for spawning. Then cut back some on the feeding. This will occur before it is warm enough for adding the tilapia. Then add tilapia later when the water temps get high enough. I would add less tilapia but put some in a protected area (blocking net or cages) and move them to the bigger pond as warranted. Make a budget using the suggestions about food types and discounts , $ for fish purchase etc all for both lakes. Be ready to reduce LMB #s in the 4 acre lake. A low dose of fertilizer may help provided it will not make the moss problem much worse. I suspect you will see this year some changes in your fish population as I bet last year you were above carrying capacity by the time the tilapia died. You may not need or want as many this year as there will not be enough room for them with all the larger surviving BG from last year.