Deleting my Recovery HD?
First of all, this recovery partition usually takes less than a gigabyte of storage, as researched online and in my early 2014 MacBook Air. You may want to look more into why your Recovery HD partition is that large.


First of all, this partition is incredibly useful if you accidentally destroy your MacBook somehow, for example deleting your MacOS. It allows you to recover and restore your MacBook without having to either bring it to the Apple Store or download the MacOS installation of some sort and install it yourself. Although, if you are concerned about your security, you can delete this partition, because others can boot your MacBook into the Recovery partition and erase your data. So it's just your choice to delete it or not.
Now, I don't think merging is a great idea since you won't be able to boot from the Recovery HD partition after you merge. The extra 70 gigabytes that are now in your main hard drive are basically a waste of space now, so no don't merge.
Here I'm not sure about this, so you may want to check with others before taking my advice. You can create a separate flash drive installer for MacOS, but I don't know if it requires the Recovery partition. According to Apple Support, it does, but I think there are other ways to install MacOS without the partition.


I hope this helps. :)