I use a sort of rolling gauge method. Need someone knocking up for you, stilts, clear room and a lot of energy.
Start laying on first load (half normal amount) (section1) and flatten off while second load is coming (normal size).
Second load acts as second coat for section 1 and first for next section (section 2). Trowel up all of it while third load coming. (this is first trowel second coat for section 1 and flattening off for first coat section 2)
Third load does second coat for section 2 and first coat for third bit (section 3). Then do second trowel up for section 1, first trowel for section 2 and flatten off section 3.
Next load is second coat for section 3 and first coat for section 4. Now you should be second trowelling section 2 and first trowelling section 3 and flattening off section 4 as section 1 should now be done.
and so on and so on......
In this way you are always laying on to a wet edge so no lines. Lots of running around and no breaks but very rewarding.
How big are the ceilings?
By the way that job has very little hardwall now I've looked at it but I could do with a hand on a "ceiling day" as I'd like to get them out the way. It'll be in November. You still interested I'll give you a call.