There isn't much a new lvl7 player with a mix of lvl6/7 turrets can do against a lvl 10 attack. That will be true as a lvl8 player, and as a lvl9 player if you are hit by a decent attacker. Regardless, I would ditch the rapid fire turrets as they are worse at everything than other turrets.
The only way I know to reduce the level of the person attacking you is to drop medals. My experience is the higher my medal count, the higher the level of the bases I attack and the higher the level of the players who attack my base. I like that tradeoff, as I can loot a lot more on lvl10 bases than I lose when a lvl10 attacks my lvl9 base. YMMV, of course.
In game name: Paper Tiger
Officer in: ThatsNoMoon
Line ID: paper-tiger