Questions about blockchains, network trust and why becoming a node? everyone,

I'm a software developer and I'm striving to understand the concepts behind blockchain and the projects running on them. I'm not sure if this is the correct place to ask these questions, but here I go:

obs: just in advance, I'm not developing a smart contract software. I'm just using it to compare

1- How many blockchains should exist? I mean, I understand that if I create my own blockchain then a new blockchain exist. But conceptually speaking, how many of them should exist for a good global environment? 

For example, smart contracts could exist in ANY blockchain? What about the actions that should occur when an event is fired and what would fire these events? The answer for these questions are a new blockchain inplementation with their own features? That would drive the answer to "as many blockchains as necessary". 

Complementing this question nowadays there are more than one big blockchain out there, right? Etherium and Bitcoin, maybe?

2- What are the nodes that compose the bitcoin blockchain network? Am I one? The miners? Who are they? 

If I create a blockchain for a smart contract solution, who would be the nodes in this network?

Why would someone become a node? What is the reward?

3- I read that the size of the Bitcoin blockchain is very very big. Anyone know the current size? It is entirely stored in the nodes machines? If not, how does it work?

4- I had a wallet in my computer, though I transferred my money to an exchange. What is stored in an offline wallet? Just a hash? A wallet is relevant for other kinds of implementations, like smart contracts? What would be stored in it?

5- I've been reading a lot about the motivation of the use of blockchains, because it decentralize the data. So I don't need to trust the government in the case of cryptocurrency. That, in the case of smart contracts, there aren't a third party.

But I still need to trust the organization behind the cryptocurrency, and there is a third party when it comes to smart contracts, that is the organization behind the software, right?! 

When it comes to smart contracts with money exchange, I have to send my money to someone. This entity is still the man in the middle. Am I wrong?

If the organization behind Bitcoin just shut doors, turn their servers off (if there are any) what would be the impact in the environment ?

Lastly what is the blockchain.info?

please, be kind
Welcome to bitcoin.SE, Victor. There are too many questions, and mostly at a very generic level. We prefer specific questions, that can be answered in a 1-to-1 fashion. This is less of a forum here. Maybe bitcointalk.org is better suited. Also: there is the webpage "bitcoin.org", and Andreas' book "Mastering Bitcoin". It is an amazing book that'll definitely get you some answers. It's freely available online here. 

I'll provide a short shot at some of the questions, if it is insufficient, just create a new one and insert a web link to here. 


  1- How many blockchains should exist?


For every use case it's own blockchain, or for everyone wanting to quickly get rich, or, or, or .... This is mostly opinion based, and not easy to answer. Better for a discussion forum.


  Smart Contracts


Bitcoin has smart contracts, since inception, and many people do not understand what this means. There is a "mantra" that only Ethereum  has smart contracts (with it's solidity language), but that's not true. In the crypto space, there are several technologies now with smart contracts, and this deserves a whole discussion chapter. Again, have a look at bitcointalk.org, and search for smart contract. Amazing discussions there!


  2- What are the nodes that compose the bitcoin blockchain network? Am
  I one? The miners? Who are they?


Before explaining the details, I reference again the book from Andreas. Generally speaking, every full node is part of the bitcoin network, and does very important verifications steps of the transactions sent into the network. The miners would make sure, that the transactions are collected into a block, which then goes into the blockchain. These are mostly the same full node clients. So you can be a miner, or you cannot. Both options are required in the bitcoin eco system. 


  3- I read that the size of the Bitcoin blockchain is very very big.
  Anyone know the current size? It is entirely stored in the nodes
  machines? If not, how does it work?


Roughly 200 Gigabytes. Think about a clock, that creates every 10minutes a block of ~ 1Megabytes in size (if blocks are full as currently), then you get 6 per hour, or 144 per day, or ~50.000 blocks per year. So 50gig per year is the growth factor in bitcoin. Data is only stored in full nodes, there are SPV nodes, that do not store the full chain (like on your mobile devices). 


  4- I had a wallet in my computer, though I transferred my money to an
  exchange. What is stored in an offline wallet? Just a hash? A wallet
  is relevant for other kinds of implementations, like smart contracts?
  What would be stored in it?


That highly depends. You need to be much more specific for us to answer this. There are many crypto currencies out there, and many wallets... Basically the wallet contains only the private / public keypairs, and some software, that is required to create transactions. (Hint: Andreas book has a separate chapter on wallets).
A wallet has very little to do with smart contracts, I'd say for bitcoin world: nothing. 


  5- ... and there is a third party when it comes to smart contracts,
  that is the organization behind the software, right?!


yes and no. At least in bitcoin world there is no organization. That is the whole deal about bitcoin. There is open source developers around the world,  and everyone can contribute. Even you :-)


  When it comes to smart contracts with money exchange, I have to send
  my money to someone. This entity is still the man in the middle. Am I
  wrong?


Yes, the exchange is your level of trust. It's all about trust: either you believe in mathematical proven code (and trust in the developpers behind, unless you are a genie), or you go to banks... 


  If the organization behind Bitcoin just shut doors, turn their servers
  off (if there are any) what would be the impact in the environment ?


The whole point of bitcoin is, that there is no organization. Look into the links I provided. Such a statement would be the worst misconception... You will find answers in the links. 


  Lastly what is the blockchain.info?


This is a company that runs a webpage with information from the blockchain (and much, much more). Their service is free of use, and very valuable if you are a developper in doing your first steps to see "inside" the blockchain.