My 5 cents:
First of all, I assume you have a CLA license, so you have a license for Deduplication (DASH Copy). Deduplication is not required by the bandwidth. But how about the amount of disk storage for the backup target? Is it sufficient if you do not use deduplication?
There are no extra MediaAgents needed, if the hardware of the MediaAgents you are using now, is sufficient for the total amount of data you want to backup (I miss a piece of information here). For deduplication, normally you have a dedicated disk however for the Dedup database (not necessary if the total amount data is small).
I'm interested to hear if from a technical point of view, there is any difference (advantage) between a remote CIFS share as a backup path for the Aux Copy, or a backup that goes from MA1 via MA2 in the remote site to the backup target for the Aux Copy. Perhaps using tow MediaAgents is better, so if one location goes down, the remote MediaAgent has access to the Aux Copy. If the bandwidth between the locations is equal to the bandwidth within each location, you could even consider a Parallel / Inline Copy.