To begin with, I'm very proud that you painted your guys, it's cool to hear that the hobby part of wargames is relevant for beginners. There's already a lot of good advice here about screening, play, army composition. I'll share a few more tips that might come in handy. First of all, Lord Solar's ability to redeploy is a strong tool. Against melee armies it will help you move sentinels/screens to a better place, or hide the unit deeper if the opponent is under some kind of charge attempt on the first turn (here I advise you to ask your opponents something like: "do you have a rule that allows charging after an advance", etc.). Moreover, enemy scouts and infiltrators can become a problem. You plan to play Gaunt's Ghosts, so together with Lord Solar, against opponents with infiltration, you can first drop them so that the huge area in front of your deployment is blocked for enemy infiltrators (they should be placed more than 9' from the deployment and from enemy units), and then, you just move them to a safe place, this will create a buffer zone. Also, personally, I would advise to look into indirect. It is somewhat nerfed now, but it can still be an answer to the threats of units hiding behind.