how much are you building? the tank itself? have atank and adding baffles? If you have the time and supplies, you have a pretty good chance at making a decent product. the chances of making a functioning product are great, whether or not it looks incredible is up to your skillset. Using silicone is fairly easy but it sticks to everything so if you dont do it right the first time itll look weird, you can cut it off and try again though so no harm there. Also they sell tools to help you make better beads with silicone. adding a sump in established tank will not harm it at all unless the silicone hasnt fully cured or you didnt clean your project up properly.