So I was browsing through Ebay, and I stumbled upon such a lighting kit:
8 x 135W 5500K Lamps Daylight Continuous Lighting Softbox Soft Box Kit Four Head | eBay (http://www.ebay.co.uk/itm/8-x-135W-5500K-Lamps-Daylight-Continuous-Lighting-Softbox-Soft-Box-Kit-Four-Head-/140889291781?pt=UK_Photography_StudioEquipment_RL&hash=item20cda7fc05)
I also saw kits with 8 or even 10 slots (lightbulbs)
Also consider a lightbulb such as this one:
Kast Lotus bulb - bec fluorescent 85W E27 - F64 (http://www.f64.ro/products/description/Kast_Lotus_bulb-bec_fluorescent_85W_E27/index.html)
It says that is has an output equivalent with 525W incandescent.

If I put 4 of these bulbs on that lamp, will I get an 2100W light?
If I put 10 of these bulbs on a bigger lamp will I get 5250W light?

Help me understand here. What am I missing?

If you put 4 of those 85W rated flos together,I do not think you will get close to a 2100W light. Flos roughly are about 4X more energy efficient compared to the common halogen filament. That is roughly. In my quick calculations the 4 flos will consume 340 watts of power as they are rated as such and will be theoretically equivalent to efficiency factor 4 X 85 watts each X 4 flos = 1360 watt equivalent filament.
If you put 10 of these together, they will draw a total of 850 watts for a roughly ( again very roughly) 3400W
of filament equivalent, again far less than the 5250W expected. Another factor to consider is the light loss in using diffusers/softbox/scrims etc. That alone will drop the output by a large margin roughly by half or more.
If they state that their 85 watt flos are equivalent to a 525 watter, I will eat my extension cable.

It would help if you described what situation you need the light for.