Will external monitor damage my MacBook? I have a MacBook Pro 2016 with touch bar (15”) and I consider making it my primary computer, as my iMac turned to be very old now. 
If I will I need to get an external monitor and for that I’d like to buy the lg ultrafire 5k. 
My only concern is I’m very worried making the MacBook a primary computer will shorten its lifespan, make it heat a lot and noisy and generally destroy it. 
I’m a software developer and I work with my iMac 10+ hours a day with heavy use thus my worries. 
If it will ruin the nacbook I’ll rather just get another iMac so it’s not a budget issue (I just rather wait for the new Mac Pro instead of buying the iMac pro now but if it’s in the cost of completely destroying my MacBook I’ll buy the iMac pro now).

Does anyone have experience with such issues or knows if I should be worried or not?
Short answer

What you’d like to do is totally safe. In fact, your MBP can handle more external displays than what you’re wanting to use.

Long answer

While I understand it, you shouldn’t let the experience of what happened to you in 2010 dictate what you do now.  For example, a number of MBP models have had faulty GPUs and you may have been using one of those. 

Regardless, to make a decision about your current setup, you need to use the specs of your current MBP to determine if it’s up to the task you need it for.

Your MBP actually has two GPUs, an integrated one (Intel HD 530) and a dedicated one (AMD Radeon Pro 455).

The important thing here is that the AMD Radeon Pro 455 has 2 GB of dedicated GDDR5 memory and is capable of supporting up to two 5K displays or four 4K displays. So, wanting to use it with one is not going to cause you any problems.

So, assuming the MBP itself is fine to run the software and/or hardware you need, then using it with an external display is not going to cause a problem.