1.The On Access Scanner scans all process activity. You may reduce scanning with exclusions but there is no specific settings for system utilization. The On Demand Scanner uses Windows Priority Control which lets Windows determine cpu usage. I would suggest going over our best practices for On Demand Scanning KB for more helpful tips: https://kc.mcafee.com/corporate/index?page=content&id=KB74059
2.Hips will usually not cause any high system utilization on a client since Firewall/IPS rules either apply or they don't so there isn't usually an abundance of processing going on. Make sure you are not in Adaptive Mode for more than the recommended testing time period which may cause performance issues with EPO and SQL.
3.There should be a way to do this with Hips Firewall connection aware groups.
4.Unfortunately this specific feature is not available. However the On Access Scanner should pick up any detections if an infected file is accessed on the usbdrive. You may schedule full scans for removable drives but that is about it.