1. I think you are probably using tab merging, correct? In that case, required fields such as ship-to and sold-to party will influence how the screen is rendered and in general, can cause unwanted side-effects while merging tabs. The following KB article should help to understand what is going on: http://wiki.scn.sap.com/wiki/display/Img/TabMerging+and+blocking+input+validation
Is your system set up so that the default tab is the Item Overview? If yes, then see this article how to handle hiding the default tab: Hiding the default (active) tab in a tab strip - SAP Imagineering - SCN Wiki
2.The area of the item table is actually driven by the backend and Personas will only be able to render it the same way like the webgui does it. You can see the same when the screen is rendered via the webgui (without Personas) so this has nothing to do with Personas itself.
Reducing the number of lines is possible but increasing the lines is not allowed by the backend. Unified Rendering should support increasing the number of lines, then it will work in Personas too.