RHP?'s
1. 80w for the 4'x2'x18" and 120w for the 6'x2'x18" enclosures - Is this sufficient or do I need another heat source to maintain the gradient in a cooler room? - heating the room not an option

It is unlikely a RHP or UTH will be enough you will need something to heat the air, as both radiant heat panels and Radiant heat tape heat air some sort of light system will likely be needed.

2. Mount RHP centered or to one side? - for best results overall
Why RHPs at all? I would suggest that if you forego the wood bottom and use PVC as a bottom. It is durable, easily cleaned, waterproof, and heats through very well so a traditional UTH could be used that eliminates some of the issues with RHPs (like safe probe placement and min distances most say 18-22 inches)

3. do you recommend proportional or on/off style thermostats? Why or Why not please?

Proportional, if you have a cool room on off types tend to have heat spikes and larger amounts of swing the accuracy is also at least 1/2 that of the proportional units and in some cases 1/4.

Doors
1. Is sliding glass or swing open better for long term use with minimal replacement?

Swing open doors are difficult to do with glass. Sliding doors are easier to use glass with although they are heavy and fragile and can be costly. Plexi scratches easily but is easier to work with and lighter. 50/50 there is no clear advantage one over the other pick what is easiest.

Thermostats
1. What temp would you set the RHP to on an on/off?
2. What temp would you set the RHP to on a proportional?

No one can say it depends on the ambient temps. I have used RHPs and would simply not bother unless I was using an arboreal enclosure. The gradient is mush easier to hold vertically than horizontally. Most of the panels on the market have min distances that are taller than you planned enclosures some choose to experiment with under this but I personally would not suggest it.

Treating or Painting wood?
1. What would you treat the wood first with as a sealant?
2. If no sealant would a latex paint be better for cleaning and uping the water resistance?

The toughest and most resistant to water would be marine epoxy, hardest to work with too. Liner polyurethane paints would be next but they too are very difficult to work with. Not to mention wicked expensive (100$ a quart last time I used any) regular polyurethane would be next, then modified urethanes (water based) latex on the bottom. Remember to bake the paint for a few days at 80º to force out gassing I would allow at least 7 days to fully cure and longer until I could smell no paint smell at all.

Lighting?
1. Would it be ok to use under cabinet mounting lights one with a white bulb one with a black bulb for day night cycle and night viewing? Why or Why not? Alternative suggestions?

I would use a FL under cabinet light white during the day but NEVER use black lights at all. Although Royal pythons have UV protection on the spectacle scale and it is not a big part of their visual spectrum you don't. Black lights have UVa,b and c. This is why people were sunglasses with UV protection, melanoma is linked to UVc It is not good for YOU. i would look to blue lights but NOT blacklight regular blue coloured LED or Blue gel over white but not a 'blacklight' bulb.

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