Here are my thoughts regarding some of the equipment. I am not familiar with all the equipment you listed, so I will only comment on the ones I know.
* biological media for the filter: SIPORAX
You don't absolutely have to get this brand (Sera), as there are others; you may just want to get cheaper biological media. Some people even use plastic scrubbers that they get from the dollar store.
* PURIGEN:activated carbon replacement by seachem. Absorbs ammonia and nitrite. makes the water clear (what is that? is that necessary? and why should i want to absorb the ammonia and the nitrite, dont the plants need them in order to grow?)
I believe many people use this not on a continual basis, but only when they need to clear up the water, etc. It is essentially for short term/temporary usage.
* Flourish by seachem, liquid fertilizer.
This is fine if you are just starting out. If you decide to upgrade to a high light aquarium down the road, you may want to change to dry fertilization, as it is much cheaper.
* Flourish Excel by seachem, liquid CO2. (does it actualy work? and if it does, doesnt it change the CO2 radically every time you use it? it isnt like a continuous flow of CO2 from a balloon...)
Yes, the product works. It is not CO2, but is similar to glutaraldehyde. It needs to be dosed on a daily basis as the molecule is not stable and degrades rapidly.
While your aquarium is low light, dosing an 80 gallon aquarium with Excel can become expensive very fast. You may want to consider pressurized CO2 if you want to go down this route (or you could potentially leave Excel out altogether).
* flourish iron by seachem, FE fertilizer
You probably do not need this as iron is provided by Flourish. This product is useful if you need the extra iron.
* Stability, stabilizes the water and adds essential bacteria. (why would i want that? cant i just cycle my aquarium for a month and get all the bacteria i need for free?)
Yes, cycling your aquarium is the cheaper alternative.
* blanki by JBL, brush for cleaning the aquarium glass (huh? isnt that what the magnet is for?)
Just stay with the magnet.
Do be careful when using it, to ensure that sand/gravel bits are trapped between the magnets. If there are, you might end up with some scratch marks in your glass.