I wish we could have more control over the backend layout of types fields in the new post editor and not locked to the 1 or 2 column layout of WordPress.
So I could have custom taxonomy and custom post fields side by side in more columns so one could build a more user friendly and logical layout.
No sure if it is possible but would be great
It is possible, surely. But Toolset does not apply a lot of customizations as you suggest, neither does WordPress natively.
Toolset usually will try to use the native WordPress setups (mainly, for compatibility reasons but also - there is no point in re-inventing the wheel).
The specific feature you request is something that is only partially possible, mixing a little of WordPress and Toolset (and for more extended control, custom code - which is above the scope of the Toolset Support).
For example, you can easily re-order most of the metaboxes in the WordPress Admin area, and they will be remembered for your user. Simply drag and drop them where ever you like - but yes, you are bound to the basic layout WordPress offers (1 or 2 columns).
With Toolset you can add CSS to the backend edit screen parts of Types Fields. This needs to be activated separately with a tiny edit to the wp-config.php File: - https://toolset.com/documentation/user-guides/css-styling-for-fields/ - Do not let you confuse by above DOC, this applies to both kind of fields (User and Post) but not Term fields.
I also requested to update that Document to be generic, for all Field Types.
These are the possibilities with Toolset.
We could file a feature request to allow more control, but this is a little out of scope for Toolset, since we build our Plugins for WordPress - and rely on it, we do not think we should invest too much in backend styling.
Also, the new project of Gutenberg is coming - it will change the backend edit screens completely. Toolset will work with the plugin. Please read more about these plans here: https://toolset.com/2017/12/how-to-use-toolset-with-different-page-builders/
