Echinodorus Barthii?
 

Has anyone kept these? If so, what is their maximum size, lighting needs, growth rate, and other information that I should know about them?

Needs nutrient rich substrate and good light. New leaves will come in red, changing to green as they mature. Propagation by adventitious shoots. Difficulty for me i would say moderate.
height 25-50 cm.
width:20-30 cm
water temp: 60.8 F (16 C) through 82.4 (28 C)
Ph tolerance 6-9
hardness tolerance: soft-hard.

Hope this helps!!!

Do you think it can hold on for a couple weeks w/o good substrate, but with good lighting and CO2 (and regular gravel)?

I cant guarentee anything but you can try it. :?

So then what about rich substrate and 1 WPG (I'll have more later)?

Root tabs is all you need. I grew a monster Red Melon Swords at a little over 1 w/g and all I did was give it a root tab every month. It literally grew out of my 10 gallon tank. Oh, and all I have is LFS gravel mixed with a little bit of river run gravel.

If I was to get another one it would over run my tank in a matter of weeks with almost 3.5 w/g and no CO2 if I gave it root tabs.

which brand of root tabs did you use? Im thinking of useing API for my stuff thats currently rotting.