SriniS,
1. Regarding SharePoint versions, your choice of SharePoint sku is not driven by Business Portal since it has no features that light up in the Enterprise sku. If you want some enterprise functionality, go ahead and use it. From a BP perspective, it has no enterprise dependencies.
2. Your BP requisition hierarchy is stored in sql. If you uninstall BP (not removing data), create a new SharePoint site, and install BP, this should give you a fresh and new SharePoint site with your old BP data.
Thanks
Rob