how deep is you sandbed???
i don't remeber the dimensions of a 55 but 40lbs doesn't sound like it would be deep enough...your on the east coast so you can probably find southdown in your area...i would add a bag to give you the added depth your sand bed needs to add in filtration...
i personally have never use a wet/dry but alot of people like them so that is definatly an option...
i always use a combination of dsb, lr, and good skimmer and have maintained excelant wq for years...if your tank is cycled properly and not stocked to quickly then the bioload won't overwhelm your system and it will adjust to each new addition...
also, i don't know if you already have the huma and eel but, i would never keep a trigger in anything smaller that a 75 (for me that would be the minimum)
hth,
mike