Patrick, can you not export as mp4 provided your film festival accepts it. I would expect your TV to also play mp4. In SMS12 either the Main Concept or Sony AVC Internet HD 1080p templates will give you 25p if you alter the framerate from their default NTSC settings.
As for your last query, with a thumbdrive your TV will deinterlace your 25 frames interlaced into 50 full frames to display. With Blu-ray players it depends on their setting. Most give you the option to choose between 50i or 50p output. The former leaves your TV to deinterlace while with the latter the player does the deinterlacing. At least that is my experience.
Personally I prefer 50i over 25p. With fast or close sideways movement I find 25p jerky. The ideal is of course 50p