This sounds really challenging, but really fun. I had a couple of ideas that I thought might be worth sharing. If you don't want to invent an alphabet of new letter forms, symbols and glyphs, it might be worth considering something like da Vinci's mirror writing to reuse the alphabet to create something that looks quite different and reads right to left. Given the complexity of assigning gender to nouns which don't have a gender another alternative might be to appropriate the set of gender mappings from an existing language, if you chose French then "boat" might be male gendered based on "bateau". If the setting is high fantasy, then the language could have a species based "gender system" that means either an elven sword is distinguishable from a dwarven sword by the article and/or having a different form (ledrows le, dudrows ed, etc), or that buildings and swords are human, trees and bows are elven and rocks and axes are dwarven.