Is this that glass you were scrounging for free? I think you said that it was 3/4-inch or something like that? That's a heavy and potentially dangerous thing to schlep around by yourself. Dropping it, falling while carrying it or smashing and breaking it in any other way...can result in far worse problems than merely breaking the glass. You're gonna get hurt.
Suction cups are great for final positioning of the glass when you are laying it onto the silicone, but I'll be honest, I don't even use them for that. You are talking about a heavy piece of fragile glass which is very dangerous to handle carelessly. I personally make sure I wear heavy work gloves and carry the sheet vertically under one arm with the offside hand adding extra support and balance. Gotta move slowly and carefully to avoid banging the ends against corners, doors, etc. Depending upon your height, you must be careful not to slam the bottom rear corner against the stairs behind you as you descend, or the front corner against the stairs in front if you are going upwards. Picking the thing up is tricky; setting it down is even trickier.
Half-inch glass weighs about 6.5 pounds per square foot; 3/4-inch is almost ten. I've carried a crapload of glass down the narrow, steep stairs into my subterranean lair, including a couple of 90x22-inch sheets of half-inch. You will be...or you'd
better be...aware that you are doing something potentially dangerous. When you are halfway up the stairs, that is a really bad time to decide that you can't go further for some reason.
TLDR: get some assistance.
Edited to add: Ah, crap, I should have known that somebody would type faster than me. Listen to
Backfromthedead
. Excellent point about the tempered glass; I'll never use it because I want to be able to drill it, but I think you said you weren't going to do that...no real need with a plywood tank...and the scrap you have salvaged is likely tempered, so that's a good thing.