Yes, that is a lot of questions with not much info
For example:
1. Do you already know if the cpu will cope with the cameras, or is it an assumption ? Have a look here for a similar system if you are unsure
https://biupdatehelper.hopto.org/default.html#stats
2. What resolution are the cameras ? It's no good telling you to record at 4K if your cameras can't do it !
3. New/Storage folders - If you have multiple drives of different sizes and speeds, then it makes sense to put BI5 NEW (And the database) on a fast drive, and to move the files before the drive is full. If you only have one drive, there is no point in moving them to another folder.
4. When to delete ? Just before the drive gets full ! I leave a buffer to ensure BI5 doesn't overfill the drive and fall over. This is more important if you are running Windows on the same drive or if you have other programs filling up the same drive.
5. 4TB isn't a lot of storage for that many cameras if they are >=HD. I get just under a month with two 1080 H264 cameras, and the two old SD cameras recording 24/7. I have just set the H264 cameras to H265 so should get more storage time at the expense of cpu loading. I have dropped the fps to around 12 to keep the cpu load low enough to allows Homeseer/ Emby/ TVMosaic etc keep working with my ancient cpu.
6. Bugs - they are attracted to IR. I turned it off for my Dahua cam, and it no longer attracts them. This cam can see in the dark anyway, having a Starvis sensor, and it sends a Lights On command to Homeseer for normal lighting as well.
The answer to your question is, there is no easy answer
