well in my opinion if u want to upgrade further, u could just upgrade ur gpu because i3 is enough for gaming, i prefer to use windows 7 to gaming, windows 8 eat more ram, windows 10 is for premium user, windows 10 still have some bug until these days, aslo if u want to check are your pc can run the game u want u can chek it here :
http://www.game-debate.com/games/index.php?g_id=371&game=Microsoft%20Flight%20Simulator%20X:%20Gold%20Edition
i wanna know your ram too, also gt 730 is a bit outdated but maybe its okay for fsx with low graphics