Sp65, I know the area well and was there touring about last week. Skiing was still available at Lomnicky Sedlo (accessible through Tatranska Lomnicka) although the lower nursery slopes had melted out. As a brief guide there seems to be two distinct seasons in the Tatras so Ican verify...
Summer trekking (May - Oct). Outside the season they shut the higher passes/routes down to preserve the wildlife and flora. Climbing/walking is possible in winter but only with guides with internationally recognised qualifications.
Skiing (Dec - Apr). Tourism is picking up and during Dec/Mar and bank holidays you would probably get a mixture of local and international bookings. Out of the holiday/half-term periods the slopes are predominantly filled by:
Weekends - Slovaks and tourist.
Weekdays - Locals and eastern European (Russian, Ukrainian) tourist.
As for rental I guess marketing is the key - you wont be competing with the hotels (of which there are many) and the Slovaks are not the best at advertising to an international market. Marketing in Germany, Holland, Czech and Russian as well as UK would expand your horizons and uptake (and translation costs)!
There are Brits who have moved out there to run B&Bs who seem to be doing ok.
Whatever you decide - good luck!
