Dont go to mustafaar! theyre may be quests that give you better xp in theory... but in practice the exp reward that higher level quests give you is capped so you lose all the benefit. What that means is when you do them out of sequence you will find it harder to level when your level is higher and you'll be faced with nothing but grinding!
Do kash, then once youve done that, theres also a few higher level quests that have been introduced (things like the azure cabal, rebel themepark if thats your faction etc). The other hurdle is the harder quests require groups to complete.
So go see the wookies, grab an xp buff and whatever else helps like armour boosts, reactive heal etc from an entertainer. Also if you lose your buff remember for a lot of quests you dont get the reward till you click complete so go buff again first if the rewards a biggie.
All this will help prolong the time when your only option is to grind(and who knows by then they could have added more quests lol).