hm, things like
"At least you wouldn't have to work that hard."
for minimum
and for maximum
"You can only at most practice for 4 hours"
The first "at least" is not the antonym of the "at most" in the second sentence. I can't find the right words to explain it in English now and I don't know how to express it in Japanese. I'm sure I've heard it alot in Japanese dramas, argh why can't I think of it now.
However, if when talking about the "at least" as in the smallest quantity or quality as a prerequisite or limit for the statement that follows it, you can use
「せめて1kmぐらい走ることができる」 - I can at least run 1km
「それぐらいできないか」 - Can't you at least do that. Both numerical and non
「とにかく食べてみてください」- Please at least try it. Non-numerical use
「少なくとも二千円だ」- It will cost at least 2000 yen. Numerical only I think.
For "at the most"
「あなたはせめて4時間だけ練習するほうがいい」- You should practice for not more than 4 hours.
「あなたは4時間より多い練習しません」 - You must not practice for more than 4 hours
「せいぜい1kgが残っている」- There is at the most 1kg remaining
As much as I study Japanese, I hardly have a chance to use it, so please correct me if any of these are erroneous.