[ACKS] Planning the Swap Rebels campaign!

After a discussion with my prospective players for my upcoming Barbarian Conqueror King campaign (ACKS Dinosaur & Wizardry AKA Sword & Lizardry), I've had an idea - rather than start the game in the current timeline, i.e. the year 3341 AS, with the City-State of Harat already liberated from its tyrant Sorcerer King and ruled by the slave-rebellion leader Hardun, why not start the game 15 years earlier, in 3326 AS, when the Sorcerer-King still reigns? The PCs will be escaped slaves, or peasant rebels, and will have their chance of participating in Hardun's Army of the Free, possibly ending up as his vassals when they'll reach name level; eventually, after 3341, they might even replace him as the rulers of Harat!

This will give the game a clear conflict to motivate things. This will still be a sandbox, and they can sill amass treasure and power (probably as part of an independent detachment fighting the Sorcerer King's forces). But there will be the backdrop of rebellion against the forces of evil sorcery.

The idea is as follows: early in their travels, the PCs, possibly escaped slaves, will join Hardun's Army of the Free fighting in the Great Servile War against the sorcerer king; they'll be an independent detachment, fighting for the Cause, as well as for gold and glory, detached from the main forces. At the beginning, this will mostly be a guerrilla war. Eventually, especially as the PCs will rise in level and hire mercenaries (or shape escaped or liberated slaves into an army) and grab power locally, and, later on. on a larger scale, as vassals of King Hardun, the Lizardman Gladiator and leader of the rebellion who'll take Harat itself.

Dungeon crawling will be part of this; after all, they'll need money and resources to fund their war, and also they will have to protect locals against Chaos and marauders (who are usually in league with the Sorcerer King).

The campaign will take place in the swaps south of Harat, where the rebels - escaped slaves - hide, and where much older things sleep (AKA Barrowmaze), and will, eventually, reach Harat itself.

The main point here I'll have to handle delicately is to preserve the sandbox and players' freedom and avoid a railroad. So what I'm thinking of doing is:

1) They'll be provided with motivation (either as escaped slaves or as villagers whose friends and families were enslaved). They could follow it, or ignore it. Or become bandits.

2) They'll be provided with background events, i.e. the growing rebellion, and will be able to participate in them, or ignore them. Or raid Barrowmaze.

3) If they do take part in the rebellion, eventually they'll be granted regional command (i.e. nobility and local rulership) once Hardun grabs Harat, as his vassals.

4) Once Hardun grabs Harat, he won't adventure much, while the PCs will probably do so, so eventually they'll surpass him in level, and if they want, they could depose of him and take power over the entire city-state. Or ignore him and go invade another city, probably with his blessings.

I'm also thinking about how to start this. One option is the funnel; but I'm not sure if the players will like it (too sharp a transition from 3.5E). The other options are:

1) They were all slaves, and the first adventure would be to escape, possibly while their masters' stronghold is under attack (by the rebels? by another noble? by monsters?). The main problem here is that I'm not sure if powerful level 1 characters would be slaves; maybe warrior types (as gladiators) but what about Mages and various priests?

2) They were all rounded up recently by slavers working for the sorcerer king. First adventure would be a prison break.

3) They're villagers. They go on a simple first adventure, then return home to find their village ransacked by slavers (under the sorcerer king's Banner of the Tentacled Eye), their families and friends mostly gone. They have to fight a small slaver garrison, and then they'll have a strong motivation to free their friends and family and take revenge.

I'm leaving towards #3, as revenge is a major motivation. Of course, they'll be free to ignore that motivation and go being bandits/raiding Barrowmaze etc. What do you think? Also, they'll need a base of operations; I'll need to find a way to introduce them to either a liberated town or a rebel camp... One hex from Barrowmaze, possibly...