Learn English – I suggest that vs I suggest doing. Does one of these sounds more idiomatic than the other

"Other than that" can be substituted here, but not "otherwise."

"Otherwise" is generally to express consequences to conditional statements (synonymous with "or else"). For example:

Bob had better study for his test, otherwise he'll fail.

It can also be used to mean "differently" or "anything else." For example:

Bob will fail his exam because he didn't study. He shouldn't expect otherwise.

"Other than that" usually means "separately," or "in addition to that" and can't be substituted into the above sentences. It's mostly used between ideas that have no direct connection, or as a final "catch-all" when listing items or actions.

Quick online search finds an answer here: http://www.thefreedictionary.com/behalf. Quoting a note on this page (all emphasis added is mine):

Usage Note: A traditional rule holds that in behalf of and on behalf of have distinct meanings. According to this rule, in behalf of means "for the benefit of," as in "We raised money in behalf of the earthquake victims", while its counterpart on behalf of means "as the agent of, on the part of," as in "The guardian signed the contract on behalf of the child". But as the two meanings are quite close, the phrases are often used interchangeably, even by reputable writers. Statistically, on behalf of is used far more frequently than in behalf of…

I would also add that "on behalf of me" sounds awkward; instead, "on my behalf" would sound a lot better. Second, in this particular phrase, using "on behalf of" seems out of place; instead you can say "instead of me" (in my opinion).