I don't know why people are telling you FX5 is the best route for you? It's definately not I have had many many problems with my FX5 ( pumps breaking, never turning back on, by passing media baskets. The filter is a mess in my opinion. Go Eheim yes the price may be intimidating at first but a 2217 with an AC110 will be more than enough plus provide stronger, more biologically effecient and a Large selection of media. Yes 600+ GPH for the FX5 but add Filter Floss to it and BAMMM maybe 75 GPH no lie. It can't even fine clean your aquarium PLUS even if you do run it at 600 or so GPH it is not giving the water enough time to touch the Bacteria making it an unefficient biological filter. However Eheim has a Moderate GPH and gives plenty of time for the Nitrifying bacteria to work as well as provides a pretty beefy water current. Also there is no filter bypass which means every bit of water that comes in hits media and gets mechanically filtered. FX5 come with circle baskets that don't seal tight and have a very poor design for mechanical filtration with having 6 foam inserts around the baskets. The foam inserts I have found DO ABSOLUTELY NOTHING. I never have to squeeze them out because they never get dirty.
I recommend eheim Strongly as well as Aquaclears. Even though AC's are made by Hagen (who also makes Fluval) they are still excellent. GREAT mechanical filters. You know when a filters a good Mech filter when it's sponges clog up quick. They are like the HOB's of Eheim lol. Very Powerful and like tanks. I have had full sandstorms go up the intakes and no harm done on an Ac 70 but yet any sand that goes up the FX5 intake it shuts off because sand gets in the pump resevoir and jams the pump instantly and it's to weak to push it out lol. Tell me how that works?
Don't be offended all you Diehard Fluval Fans out there but I have never had any luck with ANY Fluval. I spend $500 on an Eheim because I know it does a damn good job and will never fail. I run all Eheims beside my Fluval and AC's. The Fluval is for water movement HAHA!
Anyways Both Bderick and nc_nutcase are correct. Bderick is right that there will be possibly no or slight mini cycle. But NC is right in that there are many places where bacteria live like Aquarium beds, Plantbases if you have live plants ( this is actually a BIG one to many people don't know this but plants need proteins and Nitrifying bacteria break down decomposing matter to extract proteins for the plants, They are bacteria blooms at the end of roots like a bulb.) and any where, where a food source is abundant. You should be OK in setting up the 120 with the whisper but what I would do is if the Whisper has a Mesh Bag or any media with it take the media and mix it with new media that was washed in Distilled, Decloronated water and it should start a bacteria bloom once ammonia and food sources are becoming more apparent. Also what I like to do if to take some grime or poop from other filters and put it mixed with the media to give a solid immediate response.
What also will get you set with your Bio is Bio-Spira from Marineland. i cycled a tank in ONE day with it with out any prior steps. The stuff works wonders! Ok I am done lol. I will post more later.
