I'd recommend moving over to Sugarcube before going any further, honestly. The format is basically dead if you look at any other HTML/Twine-based game.
More or less, yeah. That's obviously up to you, though.You mean redo it with Sugarcube?
how can I upload it to gamcore.com?
Yellow on black is what provide the highest contrast, but on a long run it would strains eyes. Yellowish white on dark blue (just a little bit of blue) is what achieve to be the best compromise on long term.Please, no white text on back background, it gives people retina burn. Try light gray on dark gray.