Learn English – Proper usage of ‘if so’ in a sentence

The words are acceptable but the punctuation is not. Your two options for correct comma placement would be:

"Could you, please, let us know when …"

"Could you please let us know when …"

The version with two commas is somewhat outmoded; the version with none is readily understandable and more contemporary. One comma alone, however, is incorrect.

The answer will depend on what function "at least" has in your sentence. Is it a parenthetical? You can tell if it makes little difference to the sense of the sentence. I'd say that was the case with your practice:

I was trying to practice my skills, at least.

But consider the following:

She was trying to preserve her dignity at least.

Without the "at least," perhaps she has other things to save. With "at least," she has nothing else left. This means that the phrase isn't an aside and as an integral part of the meaning of the sentence ought not be separated from the rest of its sentence.

But these things are a matter of style.