3. Very limited gas budget
From my understanding, gas is not really a term used in Algorand. Algorand uses the term fees, which are very cheap per transaction. For instance, most Payment transactions require 1000 microalgos, which is less than $0.10 at the current market price. You can have one transaction in your grouped transaction pay for all of the fees in the grouped transaction.
See this post: Dealing with fees in smart contracts - #4 by javier0rosas, where @fabrice explains how to deal with fees in grouped transactions.