If you have any reservations about the existing silicone then I would encourage you to reseal it if that is something you think you can handle. The last thing you want is a tank full of livestock leaking. Yes, silicone will be inside the tank but once it is cured it will be fine. I like to use black silicone when I reseal one it just looks cleaner to me than the clear.
Aquarian is right on the light. So decide what you will want to grow as far as corals and we will be able to give you ideas on your lighting.