Hello,
Please see below for some tips on these customizations:
1) Technically, since you can customize this from various areas, there are a number of ways to do this. Here is one way. Go to Customize-->Tabs and “Edit tablinks” for the Sales Center. Add the “Customer List” as a tablink. Then go to Customize-->Tab Groups/Roles, and remove the Customer Center from the Sales and Marketing role. Then assign your sales reps to the Sales and Marketing role and that role only. They will now have access to the CRM but not the transactions.
2) Yes. Simply create a copy of the Customer List screen in Customize-->Screens. Edit your copy of the screen: find the “IsLeadStatusOnly” checkbox, edit it, and check the box to make it checked by default.
I hope that helps. Please let us know how it goes.
Thanks!