I haven't tried this recipe yet but have made similar items. Yes, I'd say it's time consuming and may take a bit of practice to get the domes to look right. Getting the mousse part to have the right texture requires attention to the proper cream stiffness and folding. If you then pour the ganache over the domes when it's too warm you may end up with a real mess.
Not impossible but you need to know what you are doing, technique wise.
As for gelatin sheets, it's just what it appears to be .... a sheet of gelatin instead of granules. Professional Chefs tend to use the sheets but you can substitute granules (by weight).
BTW - You may get more responses if this is asked on the Scrapbooks and Recipes Board too.
