This is the first time I've genuinely tried optimizing a class, within the limits of a concept. I want this character to be an Oradin, but the main draw to Holy Vindicator is a ruling my GM made when I discussed what I was going to play:
They ruled that Holy Vindicator's Channel Energy stacks with BOTH life oracle and paladin, meaning it does double-duty on channel progression.
While this looks like a cool combo on paper, it's actually much weaker in practice. Even with this combo your Hospitaler channeling will be at a 6-level disadvantage and your Oracle channel will be at a 4-level disadvantage, which is a pretty drastic hit. The Phylactery of Positive Channeling does make up for some of this loss, but it occupies the same slot as a Headband of Alluring Charisma would, which eats into your uses-per-day of channeling as well as their DC's (not to mention Divine Grace saves and your Oracle casting). It's a seriously double-edged item that I normally don't consider a viable PC selection.
At the end of the day, you'd be much better served by maximizing spellcasting power. Dropping Paladin down to 2 levels and taking the prestigious spellcaster feat will add up to 5 additional levels of Oracle spellcasting over the course of your career, giving you access to spells 2-3 levels higher than you'd otherwise have in addition to 8-13 extra spell slots. You'd still have a great channeling from your Oracle, and everything you lose in terms of the Hospitaler channeling is made up for twice over in terms of high-level spell slots. Not needing the Phylactery of Positive Channeling (since your Oracle+Vindicator level will be higher, your baseline channel damage will be significantly better) is also a huge benefit, letting you use a Headband of Alluring Charisma for better saving throws and DC's.
I don't know whether that strays a bit too far from the concept for you, but there's a lot of potential to drastically improve your spellcasting power on this build while still keeping powerful channeling options.
Would you recommend Paladin 2, Oracle 3 then, entering Vindicator at character level 6? My main concern is losing immunity to disease effects from Paladin, because some of those can be really debilitating.
It would have to be Paladin 2 / Oracle 4 to meet the BAB +5 requirement, entering Holy Vindicator at 7th. This would be my recommendation, yes.
If you're concerned about disease, you could always take the Remove Disease spell. Between that and your Divine Grace saving throws you should be able to save against disease most of the time and simply cure it on the rare occasion you roll poorly.
Human) Fey Foundling
1) Extra Revelation (Channel Energy)
3) Alignment Channel
5) Selective Channeling
7) Quick Channel
9) Prestigious Spellcaster
11) Prestigious Spellcaster
13) Beacon of Hope
15) Divine Interference
The Prestigious Spellcaster feat requires the Favored Prestige class feat as a prerequisite, so that's an additional feat you'll need to fit in somewhere. It's very feat-intensive, but the additional spellcasting is extremely good value for those feats.
I'd likely also end up going sword and board, since without Power Attack, there isn't much reason for me to wield a 2-Handed weapon. I guess I could take a reach weapon, but still.
This does make sense; Vindicator's Shield is a great feature. I'm not normally a huge fan of sword-and-board, but this is a situation where the build really calls for it.