Gestalt (Again, maybe for good)
 

I'm already aware that the gestalt rule by itself won't happen in HL. But I need to make some Gestalt Variants (or complete classes) for my current game.

Does someone knows what is the simplest way and/or have some advice on the subject? Something that can make my work easier?

Or, yet, does someone have an interest on the project of building the gestalt classes for the Community Pack? I can help with the little I know about using the editor (that I do plan to increase o the next weeks).

There is no easy way to make a Gestalt class in d20 HL. Options include using Class variants or creating entirely new classes incorporating the abilities of both. Personally, I'd probably go with Class Variants. At least that way you're starting with one class already being done. Some classes are hard to replicate, too (like Rangers), so those classes are good options to use as the base.

Is it possible to make two distinct spellcasting progressions to level up simultaneously?

Possibly. If they are different types. Never tried.

Tried this at one point. A class has a specific spellcasting progression unique to itself, you just assign its type and preparation method. You would have to add a second tab with a unique class id to get a second progression.

I've had to do that twice, it is complicated as f&% even with the experience I have

If it interests someone, I am working on this myself and once the first batch is done I can share with the community here. There is not a lot of coding, but I got enough used to the Variant Class process for this work.

For the two casting progressions I had to improvise. I created the Fake Classes, classes with complete spellcasting progressions for each basic spellcaster class and nothing else, and the Fake Caster Template whose only feature is to give a -1 ECL to compensate.

Then I tackled the 'add power/magic' feature on every but the first level of the gestalt variant. The end result is a hero with all the tabs working correctly, but it needs permanent adjustments to correct final HP and Skill Points and an eye on correct levels for feats and ability increases.

Maybe someone can help me cleaning up this with some coding, a skill I lack myself, but overall it is working better than simply have to keep track of an entire spellcasting progression by hand.

How can I make the variant count for pre-requisites?

Depends on the pre-requisites. You'll need to be more specific before I can answer this question.

Since most of the time I giving the abilities just by marking them, the one problem I got was with feats and variants that require a level in Sorcerer, directly.

The problem will also repeat for the Fighter's exclusive feats.

You'd have to use the variant to add the appropriate tag (ie Classes.Sorcerer). I've never done this, but I don't see why it wouldn't work. You'd probably want to do it some time in First.