guys, can someone tell me. Sintez is a long-term investment so i dont want to sell it too early. will i get an option to hold tokens on cold wallet?

You absolutely rightly noticed. This token will have a high demand on exchanges and, accordingly, will grow in price.

It may become "so special" in Future. Vitalik Buterin and his team announced that they are planning to burn some of ETH. In plans to take fees from app based on ETH blockchain. 

https://twitter.com/YobitExchange/status/928011407047774208
really embarrassing an exchange like yobit too hype with this segwit2x and in fact does not happen, sad

Read attentively the whole information placed on this page. https://sintez.global/ .

There you will see that the project was founded by Roman Bakulin and Roman Turev. They have been working with cryptocurrencies for over 4 years. Valery Chesnokov, their SQL developer is known already for creating successful Russian start-ups:  FL34.ru, delaem.pro, faberland.ru.

I wish somebody can find more detailed data about the other members of this team.

I believe the graph you posted applies only to stage 2.

I think the goal for both stages is a total of 13000 ETH:

Stage 1 (pre-sale) of ICO has a goal of 3000 ETH.
Stage 2 (main-sale) of ICO has a goal of 10000 ETH.

I think it is merely coincidental that there is a shift at 3000 ETH in the graph.

As to the bonus, one must wonder where the bonus coins come from? Let's take stage 1 as an example.

The ANN states that stage 1 will offer 250mln tokens (COIN) and will end when the goal of 3000 ETH is reached.
One must assume all tokens distributed during the stage 1 pre-sale must come from the stated stage 1 supply of 250mln tokens.

Therefore to cover the 100% bonus one must assume that of the 250mln tokens available that only 125mln can be sold. The remaining 125mln tokens are reserved so that they will be used for the 100% pre-sale bonus.

The amount of ETH collected remains the same.

With no pre-sale bonus:

      250mln tokens
    -------------------- = 83333.33 tokens per ETH (average)
          3000 ETH

With 100% pre-sale bonus:

      125 mln tokens (sold) + 125 mln tokens (bonus)
    ---------------------------------------------------------- = 83333.33 tokens per ETH (average)
                                 3000 ETH

The end-result is the same with or without the 100% bonus.

-------------

For the main sale it was a little harder to calculate due to the variable bonus. But fortunately we don't have to worry about the bonus because as we saw above it doesn't affect the end result:

    500 mln tokens
 ----------------------  =  50000 tokens per ETH (average)
       10000 ETH

Final summary based on stated goals and available supply at each sale stage:

Pre-sale: 83333.33  tokens per ETH (average)
Main-sale: 50000 tokens per ETH (average)

I specify (average) next to all my results because one must assume that deals will be made with large investors and will ultimately decrease the tokens per ETH for smaller investors, but I would think this is pretty normal. All I know for sure is that if I had 300 ETH or even just 30 ETH to invest you better believe I would negotiate a great price.

Everything I said might be completely wrong as I don't know much about how ICOs operate so please correct me wherever needed.

Thanks! And I think this is a great project, with or without a pre-sale bonus..

I just want to ask. If I decided to quit my signature campaign but i'd finish the task for a week, should I still get the stake corresponding to that week?

Very important question. I am also confused about this point.
According to white paper, the first stage starts 7-november and here on website it says the presale will start after 8 hours, which means presale should also start 7-november.
How many days will 100% bonus remain live?

But this kind of situation will not happen at all, as you can see they have good marketing techniques and many already trust this project.