I know you didn't ask me about what filter I use...But I bought the Fluval 406 (100 gal) and it's amazing (I wanted a greater return- I just have to hold the tubes in place)- I highly recommend the Fluval- a smaller one should be just fine, I just spoil my frogs

I didn't think the deep substrate was a problem because I do mix it up on an almost daily basis, just to get my frog out so he'll eat (yes, he loves to burrow that much and that deep- and no, the heat isn't too high). I do think that for the size my current frog is, I think I might do the sand/big rock/ and then the substrate and then wean off that as he gets bigger enough to handle all the space.
You should've seen my frog when he first went into my 75 gallon tank-it was so funny, he was hopping all over, hunting and eating all the crickets, and then he tried to jump into the background I have set up (I think it might've confused him).
Anyways, thank y'all for the feedback. I really didn't think the deep substrate was a problem, so thank you guys for confirming!