OK. This is all I can do.
I went ahead and spoke to Blue Host Customer Service. As I suspected there was nothing they could do. It was a software issue, they told me.
I found out that Blue Host has Simple Scripts, and they allow you to install Zen Cart directly from their server. Great! No way I can mess up if they do it. So I reinstalled Zen Cart directly through Blue Host. They only had version 1.50 so I installed it. Checked it. It came up fine. I did not upgrade to vs 1.51. I immediately installed backup_zc_v1.1 according to its instructions. I then logged back into admin, Tools menu, and it was not there. I then installed backup_mysql_plugin_v1-5 and went through the same cycle. And it was not in the Tools menu. I didn't even bother trying to install chaddro-EasyPopulate-4.0-f4314dc.
I've done everything under the sun, according to the instructions you gave me; and have spent an awful lot of time, and nothing works.
If none of these work when the Zen Cart 1.50 is loaded by the hosting company then something is really amiss either in the plugins themselves or the instructions.