The way i determine the light levels for my Roths is to look @ leaf colour.
I grow mine with quite high light(Catt level) & the leaves have a yellowish cast to them , as far as my research has gone this seems to be about optimum for growth.Good air movement is essential & will help keep the leaves cool so you can give it more light .I have actually measured how much light they get & it,s about 2500/3000fc in my growroom & upto 4000fc in my g/h.In the growroom they get this light for 12 hours a day every day , in the g/h they get 4000fc occasionally but have light for a lot longer.
For potting medium i have gone for the fast drying(med bark/leca or med bark/perlite) & water every 2 to 3 days depending on the temp.
Roths in active growth need regular feeding , they don,t seem as susceptable to leaf tip burn compared to some other paphs.I add a lime substitute as a top dressing(calcified seaweed) , this is a natural product that should help supplement calcium & magnesium.My fert does have these but since i fert @ lowish levels they might not get the required levels.
If you have other paphs feed/water them like the others.
My large Roth(just putting out second growth) cost me £120 last year
($220 ) & the other 2(a little bigger than yours) cost £30 each(about $55).
I,m waffling.
Basically upto Catt light , good air movement , free draining medium , water so that it never dries out , fert @ the same level as your other orchids ,flush the pot to remove any salt buildup , consider supplementing calcium/magnesium.Plenty of articles on this you make your own mind up about supplemental calcium/magnesium.
I do as this also helps to buffer ph of the medium.
I,m still learning about these guys even after 18 months of research & growing them.