Will the Xappex - G Connector app be able to create a "Percent of" column?  For example, my client is requesting a custom Balance Sheet and Income Statement with a Percent of column.  See example below.  Custom Financial Report Definitions does not have this capability.  

Here is a link the documentation for the formula on Xappex.com's website:  https://www.xappex.com/docs/g-connector/basic-features-g-connector/integration-with-accountingseed/

I was able to build my custom P&I report. But periods have to be closed for YTD to work. And the loading times are excessive when loading more than a period or two.

No. The custom report generating tools are very difficult for such an expensive program.

Have you found any good resources on it?

It would be great if Accounting Seed produced a knowledge base article on using this tool.

This way usage instructions would show up in searches on the website. 

For example, it took me a couple of tries to realize that the "YTD" term only works up to the last closed period. If you include an open period in the range, the YTD values are incorrect.