We are all "crazy aquarium guys" and girls, it comes naturally when you see the diversity of life from the sea that you can enjoy in your home. I am the same way with multiple tanks, when I get all the tanks set up that I have accumulated for next to nothing over the last couple of years my house will look like a pet store like it did 20 years ago when I was deep into freshwater. As you already know from your other tanks, you can always find a use for one more smaller tank when you upgrade.
The best advice I can share is to find a local marine aquarium club and join. Ours has meetings most of the time in members homes and new people get to see all different kinds of set ups and equipment use (there is no one "right" way) to decide what they want. The diversity of people in the hobby will give you the opportunity to meet some who are very successful financially and can afford top of the line set ups as well as those like me who do it with very little expense but avoid the "junk" that doesn't work well. Continue to post here regularly and take advantage of the experience available at a national level but get involved locally for hands on help you can see in person. Hopefully you will meet someone with a set up similar to what you want that can become your mentor.
Local clubs usually have a selling forum on their site that you can find used equipment on for a fair price from trusted members. They will also have postings from people that drift in and out to sell the junk you have found on craigs list or good used stuff that they want too much money for so be careful as you already have been. There are good people in this hobby who join a club to socialize and help others that are new but there are also some who join with an attitude of what can I get out of these people and not give anything back.
My experience with buying used has shown me that very few "complete set ups" sell well. Sometimes they are bought by new people which can work out for everyone involved if it is a good set up with no problems. You will find deals "$2800 invested, $1500 for everything" that sound great if you were planning to pay new prices. Maybe in todays market it is only worth $1000 (even new stuff is very low cost right now with the economy) and maybe the person got into the hobby recently and is getting out due to failure caused by buying junk equipment you will have to replace. The rock may be covered with aiptasia or other pests that will take a lot of work for you to turn into a nice tank. Most tanks end up getting parted out. Experienced reefers will buy only the good equipment if the price is fair and leave the tank since they already have one. There are a lot of tanks and stands left over out there that can be bought alone for very little money. You can then shop for quality used or new equipment to put together exactly what you want.
There is a lot of "brand new in the box" powerheads etc. out there that people in the hobby (who change their mind a lot) are getting rid of. There are also things out there being sold because they have worn out and only run at half speed and the owner bought new instead of repairing what they had. I have bought BNIB $70 powerheads for $35 but before I knew better I bought $30 used for $10 that are only good for mixing saltwater. New technology BNIB stuff costs more but is worth it if you were going to buy new anyway. An MP40ES is $465 on line and you can find them for $400 or a little less BNIB not half price like I have found on smaller older technology.
Good luck with your new adventure and you made a good choice on the small tank to learn on. It would have worked out fine if you had started bigger due to your research and questions showing that you are the type of person that will be successful long term no matter what size. You will get a lot of enjoyment out of your new tank as long as you continue the patience you have shown.
( Or so I hear) I am so confused as what to do... Grr...
I think that waiting until you find what you are wanting for the larger tank is a smart choice and until you find it the biocube will give you the chance to get started in sw. I agreee that keeping an eye on local forums is a good idea and if you can get involved in a local club I would do so. Also with the biocube you might consider getting involved with the nano in 90 contest that is taking place 
.. night = giant..
