All great questions, data recovery is something I am quite familiar with.
A1. 5 beeps from a Dell, is generally bad CMOS battery, might be worth replacing the CMOS battery. Here is a write up from Dell community.
The fact that your chkdsk process has hung at 74% reflects A) you disk is faulty B) You have massive data corruption. It is never a good idea to interrupt a chkdsk in process as you further risk data corruption, I have waited up to 24 hours for a chkdsk process to finalize.
If you have already placed your old internal disk into an external hard drive enclosure and nothing is popping up then you have lost your partition tables.
If you truly care about or require any of the data on this disk then I highly recommend professional data recovery as you are risking it all attempting recovery yourself.
If you choose to attempt data recovery yourself you can try using Test Disk, which I have successfully rebuilt lost partitions in the past with. Here is a step by step guide on recovering an NTFS partition along with individual files Here you can download the program.
If you are able to restore you lost partitions, then immediately start working on getting your data off of that drive.
A2. While there is not need to partition the disk to restore 2 sets of backup data (could use two folders to separate) You can partition a disk with data on it buy using a third party program, here is a write up on it. However you risk losing all data if you make a mistake.
A3. The red bar indicates that your disk is almost full
Best of luck, let us know how it goes.