Having done more times than I like to admit, smaller tankls work out fairly well, I'd shy away from the 29gal size though.
A 20 H or a 10 gal is fine.
The Oceanic 30 cube will work.
I used a jack to pop the last bit off. It's not an easy thing to do.
Generally, most folks like the custom made glass tanks.
But if you are cheap, popping them off may be right for you.
If the tank bows, then you'll need a glass center brace, still looks better than that ugly rim.
As far as globs of silicone.........you will use a razor to cut and skim the silicone away.
Do not rush or force things too much. Take your time working the rim off from both sides.
Larger tanks like a 75 are more difficult.
Do not do tall tank or very long tanks without braces.
You can have these braces made for a few $ at most glass shops.
Use a couple of grades of sand paper(power sanders are the best for this) to create a nice smooth edge.
You can add the brances on top or on the inside of the tank also.
Use tape to cover the areas you do not want silicone on and make sure you have plenty of pressure on the seals while they dry and give the full 24-36 hours for the full cure.
Use only clean razor blades, these will never scracth the glass.
Regards,
Tom Barr