If you are exporting to Xero they do recommend that you restrict your batch sizes to ensure a timely response from the API service. Large batches can take a while to pass through the API process to it is advisable to work with smaller batches.
Here is a link to their blog on the subject:
We recommend a limit of 100 candidates per payroll batch (this means that you can have multiple timesheets for the one candidate in the batch and it will only count as 1 towards this limit). This is due to Xero limiting the amount of requests we can make to their API in a single minute, limiting your batches means that you won't receive any errors messages.
Regarding invoice batches, you can have as many invoices in a single batch, as we send them in groups to Xero to ensure they are under this limit as well, so if you are processing a large batch, there may be a delay until your invoices appear in Xero.