It is tough to do a rough guess on a mobile home, because your construction and insulation are different, possibly minimal. How many BTU is your furnace? I am guessing it may be relatively small, in your climate. You will have to determine from the manual for that heater how many tons of A/C the blower will support. But since you are well under the 3 ton range, it is likely that will not be a problem. A local HVAC guy should be able to figure this out.
Yes, you need a cased coil attached to the furnace. Is there room on top of the furnace for that, where it sits?
Around here, you could get the coil and a 1½ T R410 condensing unit , installed, between $3k and $4k.