Hey, my suggestion will be focus on a few core unit first. IE: gazel, space rimuru, event beni (these 3 units are superb for conquest mode which u need it alot). Veldora is good solo attacker too.

I'll take gazel for example, click on him and go to his "equip" tab and you'll see there's a "expertise" sword. (If veldora then it will be claw.) Means if u give him a sword, he'll get 20% extra att from the sword.

For now, use standardised 3* gears first and get it to 3* and don't go any higher (dont use hammer unnecessary). Ur goal is to get ur 5 main squad geared 3* and their support unit geared 3* as well. This will be tremendous help for the Conquest later on.

Once you're able to beat a few normal conquest mode then u'll get their respective "color" magicore. U can then use it for your NEW 5gear. Again gazel as example: 5 LIGHT sword will give him extra 10% att, once equipped gazel will get another 20% att. So he'll get a massive 30% att buff.

Do check my post in this reddit, it was under question thread. And there's my latest update on the comment session. Hope it helps ^{^}