I haven't heard of such a problem before. Does your server maybe limit the supported authentication methods?

Please try to enable the "Debug Log" setting in the connection's settings screen. Tap on the (i) button on the right side of a connection to change its settings. This creates a log file when you try to connect to the server which might help you find out what's wrong.

Textastic for Mac does not currently have regular expression search and replace. Only the iOS version supports it at the moment.

You need to go to the Remote Transfer screen again using the "globe" button. Then you connect to your FTP server, navigate to your target folder and select the local file on the left side. Tap on the Upload button to upload the file to your FTP server.

You only need to do this once per file. From now on, Textastic will save both the Dropbox and the FTP remote location and asks you which one you want to use when you use the quick upload feature ("Upload This File"): http://www.textasticapp.com/v5/manual/lessons/How_can_I_quickly_upload_downloaded_files.html

You can use the "Open…" command in Textastic (below the selection between "Local Files" and "iCloud") to open a file from Working Copy.

Please have a look at this blog entry and video for details: http://blach.io/2015/05/26/using-git-on-your-ipad-or-iphone-with-working-copy-and-textastic/

The name of the theme is actually taken from the "name" key in the .tmTheme file. All themes have the same name:

<key>name</key>
<string>Kachun</string>

Please change that string to match the file name and it should work.

Can you send me the file(s) so I can try it on my Mac?

You cannot run Swift code on your iPad using Textastic. The preview (glasses) button opens a web view and allows you to preview HTML (Javascript, CSS) and Markdown files.

Yes, please. You can send it by email to support@textasticapp.com

A step-by-step guide about how to reproduce the issue would be nice.