Am I receiving a fair amount or should I get a mediator?

After being married 24 years, my husband decided to move out because he doesn't love me anymore. We have 3 boys, oldest 23 just out of the Marines and at home until he gets settled; other son, 19 is in college with a scholarship; youngest son is 12 and is high functioning autistic and intellectually disabled and will never be self sufficient. Husband took over our finances after I had handled them for 20 years about 3 years ago. Long story short, we lost our home that we lived in for 20 years. Moved out of town and are now renting a home. Shortly after moving, our boat was repossessed as well as one of our cars. Husband retired right after our move, works and makes approximately $3000 a month as well as receiving a pension income of $3179. It was agreed 8-9 years ago, I will quit my career and stay at home for our son. When he decided to leave, I suggested I stay in our home so that we don't interrupt our son's schedule and break the lease which we've signed for 3 years. We have been renting for 18 months now. The rent amount is $1350. Husband offered $3000 in good faith. With the rent, utilities, unpaid bills and groceries budgeted at $150 weekly, the left over amount is approximately $178. My autistic son attends a Shelly Baird class and his breakfast/lunch money is $100 per month. He also sees a psychiatrist 2x a month which costs $20 a visit plus gas traveling 50 miles one way. His medication costs $70 per month. I'm concerned for his stability. Husband wants visitation every weekend of the month. I do not agree to this. Husband suggests I have him 1 weekend, still don't agree to this. My son is very structured, and I have gone through behavior therapy with him for over a year. I have continued with the program and he responds very well. However, husband does not use the program which causes meltdowns at times. My question: without sounding greedy, is this a fair amount; should I get a mediator because this is all agreed in good faith?