Please help

[Rpbarber]

Trying to start my third commander deck with  {Progenitus}. I have never used all five colors before. What would be a good frame for him?

[Gorzo]

I suggest focusing on two or three of those colors mainly, and just splashing the last ones. Green will likely have to be one of your primary colors, offering you the best mana fixing around with spells like {Cultivate}, {Harrow}, {Channel the Suns}, and {Shard Convergence}. Also make sure to include many multicolored lands and a {Chromatic Lantern}!

You may also want to consider using the blue to counter wrath effects, as they are still able to kill progenitus. It's a good idea to know your own Achilles Heel, so you can protect it properly.

And if you don't run {Door to Nothingness}, I will be very disappointed

[Rpbarber]

How many lands should I be running? And what should the split be between basic lands vs. non basic?

[Mactitioner]

You want to figure out what your win con will be...  {Helm of Obedience} +  {Rest in Peace} is a solid win con for any deck with the option to run white. I would run that for sure for one option.

[Gorzo]

How many lands should I be running? And what should the split be between basic lands vs. non basic?

40 lands. As for how many basic or nonbasic, that's entirely up to you. Dual-colored lands are better for mana but can potentially be slower by coming in tapped. Balancing speed and efficiency to your play style and to match your group is up to you.

And your budget. Nonbasic lands can get expensive.

[Vileo]

Tip: {Gaea's Balance} if you're mainly running basics.