I know this probably isn't what you want to hear, but I wouldn't worry too much about being very competitive just yet. The first thing you need to do is get all those legendaries up to at least level 50. That will maximize their gold production, allowing you to grow more food, allowing you to level them all up even further. If you don't have your boosts built, build all of them to help with the gold production. If you don't have your temples and farms upgraded all the way, do that (and then grow as much food as your gold income will allow). Once that all happens and it's easy to immediately get a monster to level 100, then you'll be in a good spot to start being competitive.
For your attack team, one of your best deniers, in my opinion, is going to be Saika. Rocigon is a good supporter and you've got a few attackers to choose from in General Nishant, Makugan, and VoltaiK (don't use VoltaiK if your enemy has a monster with anticipation though, although I'm guessing that's less of an issue in whatever league you're currently in).
I actually don't use a strong defense team. Instead, I use a single common monster. This way I can get a lot of relatively easy revenge attacks. I only change up my defense team the last day of the PvP season. Keeps me in my league quite easily.
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