To answer the original question. No you do not have to open a HSBC account. The reason they suggest it is that HSBC in hkg is as ubiquitous as McDonalds and Starbucks combined in the states!
When I was based offshore I used to get a demand draft (bank cheque in pilot english) as that was the cheapest way to transfer. You pick up the cheque and deposit it at home and usually it gets cleared immediately. If you are going to be a freighter fo etc then HSBC is a good option as there is a branch in the CX building.
Minimum balance....hmmmm... there are a few different accounts called premier, power saver etc. If you are going to use the bank like 2 times a month just get a regular savings account...especially if you are based. you can do all your banking online anyway...you can set up telegraphic transfer accounts to cover those times you are not in hkg for a while.
If you do a monthly demand draft it should cost you less than 100hkd per month to take the money home!