Move HVAC package unit near crawlspace to split unit on to attic

[Gp G.]

Hi,

My property is built in 1961. HVAC unit is package unit on right side of the unit. Duct works goes from package unit to crawlspace to bottom of the floor to the unit. Duct work is old metal ducts. Air filter also in crawlspace inconvenient for tenants to change.  Package unit not sure how many years old as it was there even before i purchase this property about 5 years ago. Some times package unit is not working and fixed few times by HVAC contractors. Also the metal duct work in crawlspace has leaks which tapped by one HVAC contractor. Air conditioned air leaking to crawlspace making crawlspace heat or cold depending on season causing more power bill to tenants. I am thinking to remove package unit and instead of that put split unit. Put the fan near the package unit area and heater in HVAC attic area. Attic area height is less like hardly 3 feet. Does attic fit the heater there with 3 feet clearance and also duct work. Is it good idea to do this project spending about 10k now. Any pros and cons of this project I need to know before I begin and spend lot of money. Hope no fire hazards or code issues or noise issues or electric shock etc. by doing this project. Please advise