If you can post your machine settings here, we may be able to help troubleshoot the Z axis issue and make recommendations for other settings. If you can give us a list of the other problems you’re having, we may be able to help you fix them.
As for the G-code, there is a beta app that will allow you to import G-code into Easel. You can go to this forum and ask to be let into the trial group, and see if your G-code works: [NOW LIVE] [new feature] G-code sending through easel - #5 by EricDobroveanu