I have a question, Why people want base (lvl5) pokes more than those unbase ?? does it mean that if i get some cool shiny/rainbow or whatever i should sell it asap ?? why people dont train those pokes ?? my mind blows ! :
Also to not make spam, second question: on which poke should i use toxic move to make the best use of it ?? i have now golurk but should I aim for colored golurk first or just use it on that normal ?

Because base Pokemon are worth more than unbase Pokemon. Think of it this way. You want to buy a video game off Ebay. Do you go for the used or new? I'd assume you'd go for the new. Same with Pokemon. Think of the base Pokemon being the 'new games', and the unbase Pokemon being the 'used games'. And on top of that, which would be worth more? The new one obviously. And that's why everyone wants base Pokemon.
And the second question. My opinion would just to put it on whichever you thought would be best.

so people who want to buy 5 lvl pokemon are super mega collectors who dont know what to do with their money yep ? because as of me now (350~level) i would pay more for 1k lvl gengar than 5lvl gengar.

I wouldn't say they don't know what they are doing. collectors keep pokemon off the market and that brings up the price of the pokemon, it's like a investment.