Hi & welcome to AA!!
You will not want to attempt the connections with silicone!! It will fail & you will get a leak....
The proper way to connect stuff through a drilled tank is with bulkheads, like these:
The bulkheads allows you to make water-tight seals through holes in your tank. For holes in the bottom, you would attach a pipe (the stand pipe) to the bulkhead inside the tank. Make the pipe taller than the water level & you can pass tubes,etc. through it without fear of leaks.
This is however, a rather complicated way to plumb a tank for your purposes. A drilled tank is really useful in sump setups. It is overkill (not to mention risk of flooding) to drill a tank just to pass your hoses through.
If you want to hide your mechanicals, a better solution is a canister filter. The filter can sit under the tank in a cupboard, and the intake & return hose hang over the rim of the tank. You can use strainer & spraybars that are almost completely hidden by your canopy. <But this setup only exchange water from the top of the tank. So some would place them deeper in the tank. In that case, you would have 2 vertical pipes visible, still pretty easy to hide.> You would T in your CO2
to the return of the canister (some build a diffuser in line with the return). Add an in line heater, and all your equipment is out of your tank & hidden.