I've never used an air fed mask, but I'm wondering if you would even need a compressor.... Mask air should be a high volume low pressure deal. Would not some sort of blower or fan arrangement work?
as for a compressor im looking at a 2hp, 50L with enough air flow.
The only problem is that its a oil compressor not a oil free one.
2hp how many cfm is it and haw many cfm will the mask be, will you be running a spray gun at the same time, if so it probably wont produce enough air for both at only 2hp