Although truthfully it's best to go to Nar Shaddaa first because if you go too late you cant get enough influence with Mira to train her as a jedi, or get enough influence with GO-TO to know everything about him. The problem though is that Nar Shaddaa is hell to play at low levels, it is actively unfun and way more satisfying to go through later.
I wouldn't say can't, BUT you do have to know specific influence points to get progress.
Mira has two specific points on Dxun
-Take to the Zhug fight and tell her she's the best bounty hunter.
-Use a permacrete charge to blow up a Mandalorian cache near the south entrance. It's not the one that Mandalore tells you to blow up. Unfortunately, there are only two permacrete charges in the entire game. One is in Korriban that you can use to blow old Uthar Winn's room (where Bastilla's holocron can be found) and the other is on the body of the droid technician on Dantooine. If you kill this Sullustan, you can't blackmail him into joining the militia and obviously killing him is a dark side action.
GO-TO
-In his dialogue options, tell him that you're grateful for how useful he is after he tells you about his body's capabilities (one time only).
-On Onderon, have him reprogram the droid that sells droid parts.
-Not really an influence point, but if you bring him to one of the bounty hunter fights on Onderon, he will tell the T'wilek hunter that the bounty's called off and you can avoid the fight. I don't recommend doing this as you also miss out on getting his Starport Visa.
As for planet order in general, I like to play Dantooine first up until the beginning of the Battle for Khoonda and then go to a different planet. Nar Shadda's point of no return is set on some weird triggers that are hard to play around.
1. You have to go to the refugee sector. Fucking around in there in any way really sets off the Exchange's radar.
2. You have to kill the Red Eclipse guys that board your ship. Note that if you've already seen the scene where the Trandoshans threaten the Toydarian, your party is locked until you liberate your ship.
The good news is that after you get rid of the Red Eclipse guys, you can leave the planet (unless you sold T3-M4) and come back to Nar Shadda at a later time where you're at a higher level. Which I would recommend because the game forces you to use Atton as the party leader and even force T3 and Mira/Hanharr into your party.
So, I generally go Dantooine --> Nar Shadda --> Korriban --> Either Dantooine or Nar Shadda depending on alignment --> Onderon