hi all...  my wife wants to start a goldfish tank but knows little to nothing about fish in general...  i am familiar with fish, just the opposite of goldfish though...  i keep cichlids...  i have a 90 gallon cichlid tank, and have had them for a few years now... 

so, tons of questions to ask...   
1. size of tank?  we have a 29 gallon tank(30x12x18tall), would that do?
2. how many goldfish?  my wife is looking at getting 3...  she thinks that is a good number...   fantails is her fish of choice.  is 3 going to be ok for a 29...
3. gravel or sand?   i heard that you shouldn't put small gravel in as they like to dig, and they tend to think it might be food....  so i put sand down.   
4. filtration?   we have, what i believe to be, an emporer 400...  it has 2 compartments...  each has a biowheel, a blue filter pad of probably carbon, and a grey container of carbon or something...  is that good for goldfish or do i need something else...
5. decorations?   they like to swim, so i assume less is better...  it is in our bedroom, so i don't want it too plain...  we have a few fake plants in there now, and some rocks with holes in them from stores...
6. fish compatibilty?   we have had our 29 set-up as a community tank for years, so it is well established, and all fish have since died except for 2 black skirt tetras...  i know tropical fish and goldfish are not a good match, but you think they would be ok together if i kept the temp up at like 75 degrees...   i know disease and stuff is a factor, and i know what the answer probably is, but just wanting to know if anyone has kept fish like these with goldfish and have success with it...

last, again the tank has been running for years now with tropical fish...  is there some drastic thing i need to do before turning the heater down to 72-75 degrees, and adding goldfish... 

i am sure i missed some stuff, and hopefully all you guys/gals will help me out through this...  we are hopefully looking to add the goldfish this week, so if i shouldn't, PLEASE tell me....

like i said, we are new to goldfish, and are unsure of what to exactly do...
thanks again...
Brent