When they meet, General Syndulla is actually prepared with his plan on how to approach the mission! Apparently Kina is no longer the only person in charge of ideas!
Given that they don't technically have authority to attack the Hutts, they will begin simply by sending a few representatives - Syndulla, Mundi, and Trebor - to meet with Jabba and search the premises. Once they find something highly illegal, which shouldn't take more than a minute or two, they can slip away to a private area and then call in the full strike. Jabba's forces, while numerous, have little in the way of aerial weaponry, so most of the attack will come from directly above - after a few droids draw away their attention at the front gate. The main force will first take the tops of the smaller towers, and fortify them as sniper positions, then head from there to the large dome that makes up most of the palace. From there, they can head downwards and hopefully make it to Jabba's throne room at the bottom.
Primary backup plans in the event that they end up outnumbered would mostly depend on just using what ships they have to directly bombard the palace, although this isn't ideal due to the potentially large amounts of casualties. One obvious area of concern is if Jabba just tries to kill them the moment they walk in, but hopefully the Jedi will be able to defend themselves and Syndulla long enough to get to safety, and if possible, take out some of their enemies from the inside. The other potential problem is if Jabba turns out to have reinforcements available from the other criminals and bounty hunters of Tatooine, but they're counting on nobody wanting to get too close to a battle against galactic superpowers, as well as just hoping they can capture Jabba before he has time to call for help.