For a 1 gallon tank I would not add any kind of "sucker fish" at all. I would go with the two ADFs. You could do half land and half water, but this would use a lot of tank space and you would be better off with just one frog who will not use the land area anyhow, so unless you want to get a semi-aquatic frog/toad, just stick with an aquatic setup. I have no knowledge of semi-aquatic frogs, so I can't say if a 1 gallon tank will be enough. The frogs don'e need a deep substrate at all, anything from .5 to 1 inch will be great, just try to make it soft sand or rounded gravel, like I said before.
For the rocks, you can use any silicone sealent, so long as it is aquarium safe. There are meany sealents sold that have mildew preventatives and other addatives that will be toxic and fatal to aquatic life, so be sure not to use any of these. Make sure any you get is either aquarium safe or safe for food surfaces. These will not have the toxic addatives.
I am not sure about plants, I have not yet "graduated" to live plants in my tanks.
\Dan