Mars as the next step is a stupid idea. And that NASA also keeps suggest it as a next step proves to me how unworthy NASA is of funding. Same whenever they keep doing stupid studies on humans spending long periods in confined areas (they can always ask the nuclear submariners about it).
The true next step for anyone serious in making actual progress in space tech is to build a space station with artificial gravity (tethers+counterweights or other).
Once you have that you can test various animals (rats, food fish, humans) at Earth and Mars "g" concurrently to see how well they hold up for months in space.
And if you succeed in making that tech practical and cheaper it means you don't actually have to go to Mars - you can colonize the asteroids.
There's no actually much benefit going to Mars in the next few decades. The "g" is wrong, the pressure is wrong - you can't really use the tracts of land for farming without effectively building a "space station" on Mars (pressurization, shielding etc) - so there's little advantage over a space station with the disadvantage of not being able to pick your "g".