I would suggest that you look at the US6.40 per point contract to determine your trades. The mini is basically arbed to it so you could trade the mini for test purposes off signals on the normal contract (I think).
I used to do that and in my personal opinion it works reasonably well.
With the exception of one type of orders: market-on-close. Liquidity on the 10HKD contract tends to disappear on the close, while on the 50HKD one it's still okay.
If you trade 1-2 lots you should be fine except if you need to execute market-on-close orders.
For orders at market you need to size substantially more slippage on the mini. In my opinion, on average - depending on what strategy you have... - 2-3ticks. This is what I had but may be your trading style/strategy will manage to minimize this...
The daily volume on the mini is very approximately and on average about 1/4 to 1/3 of the Bid contract.
