1. Resteem is perfectly safe. It does not affect your reputation (good or bad). It does tend to steer you audience away from your blog.
2. I don't use any chat messenger for STEEM. There are several Decentralized apps called Dapps built on the STEEM blockchain. You can use any one of them to blog onto STEEM. Each one has a different interface, allowances, and options, but they all use the same STEEM blockchain. For instance you post something using steepshot, the post is accessible from Steemit or Busy. Each Dapp is built by different individuals or teams and language options may not be available. There are also Dapps out there that take your existing twitter, instagram, or facebook post and copies your post and creates a post on your STEEM account. I can't tell you what the Dapps are because I don't use them. I just know that they exist.

You must be careful of plagiarism. You cannot copy other people's work pictures, video, or music. If you copy and paste some sentences, video, or pictures from another person or website, you must cite (reference) the source. You also cannot just site your entire comment or blog. At least 50% of your blog must be of your own creation. If you are caught, you will get put on a blacklist and it is extremely difficult to get off. If you are on a blacklist and continue, your reputation can be severely damaged. Some blacklists don't allow second chances.

If you use a Dapp that copies your Twitter blogs (for instance) and creates a Steem blog by proxy, you must make sure you reference anything that is copied and make sure that at least 50% of the content is your original work.

Here is a link to the guide that you can use to avoid a blacklist
https://steemcleaners.org/abuse-guide/