wondering if the upgrade will be worth it

With 2 dual 4ohm subs, you can wire them parallel/parallel to 1ohm. This will get the full 1000watts from the Cadence. There is now way to wire all 4 coils to 2ohms.

You'll have about 4 times the power, so you'll gain about 6dbs.

What vehicle? What box are you using? You might be able to build a ported box and get about 3 more dbs -if you've now got a sealed one.

You can, if you don't have a bunch of other acc. on at the same time.

You'll at LEAST need to do the Big3 upgrade. https://www.the12volt.com/installbay/forum_posts.asp~TID~73496~PN~1 in  at least 4g wire all around. If you need a lot of other acc on while your system is cranked, it'd be a good idea to invest in a HO (high-output) alternator.

Find out what size fuse(s) the amp has in it. -I couldn't see anything.

Use this guide, based on total fusing in the amp and the total lenth of wire needed from battery to amp, to determine what size power/ground wiring you'll need. Bigger is always better though.

https://www.the12volt.com/info/recwirsz.asp

*Pay attention to the max amperage the wire you'll use can support and fuse it at the battery with a fuse of equal or less value than what it can handle.