After having done some research, I managed to find a solution for most crashes and low FPS issues.

It seems like the reasons as to why the error and crashes appear, as well as the low FPS on some occasions are all due to several programming faults within the ReBirth3.exe file.
The .exe file doesn't have the correct instructions on what to use of the OS, and just pushes the default instructions out, which eventually cause the game to crash or have a low performance.

-
The most common issue, as people have previously pointed out, is the 2gb RAM cap.
It seems that the .exe is instructed to stay bellow a 2gb RAM usage; which in turn will lead to a crash once a heavier scene appears.

The way to fix this is by changing the code in the .exe file and forcefully make it so that it uses 4gb of RAM or more.

The CFF Explorer program used in order to fix this can be confusing, and for the people that (like myself) don't really want to install it just to be able to play the game, through this link you will find a Patch, which is written by the developer's of the CFF themselves, that will change the code of any .exe you want from having the 2gb RAM cap to being able to use 4gb or more:

http://www.ntcore.com/4gb_patch.php (64bit only)

Just download the zip, run the executable, choose the ReBirth3.exe file to patch it and you'll be all set.
This Patch will also automatically make a backup copy of any .exe file you choose, so you'll always have a safe version.

This way you will get the ReBirth3.exe fixed without having to install the CFF program or run through all the steps.

-
Now for the next issue, it seems like the ReBirth3.exe file is also instructed to run on a integrated graphics card by default instead of changing to a dedicated one in most Laptops.

An example for this is having a Intel HD Graphics 3000 as the integrated one and a NVIDIA GeForce GT 540M as the dedicated one in my case.

The ReBirth3.exe is under the instruction to never trigger the usage of the NVIDIA card, unlike ReBirth1 was, and will always run on the Intel card, causing the FPS to drop bellow 30 on a constant level or even crash during heavier loading scenes such as the common Plutia battle one.

-
In order to fix this you will have to manually add the ReBirth3.exe file in your NVIDIA control panel and choose to run it in a high-performance NVIDIA processor setting by following these steps:

1. Open the Windows Start Menu
2. Enter “NVIDIA control panel” into the Search field and run it
3. Select “Manage 3D Settings” from the option in the left-hand panel
4. Select the "NeptuniaReBirth3.exe" to change the graphics processor for the game under the "Select a program to customize" option
5. Select your NVIDIA graphics card under "preferred graphics processor" instead of the default “auto-select”
6. Click Accept and you should be all finished

With this, the next time you launch ReBirth3, this should properly trigger your dedicated graphic card instead of your integrated one.
Not to mention that you should now be able to play the game at a stable 60FPS and without any crashes.

-
It should also be of notice that you should have the latest Visual C++ components and graphic drivers up to date in order for everything to function properly.

-
At this present moment with these fixes am I am able to run ReBirth3 on my old laptop without any major issues, so I hope this simple guide will help you run it as well.

Thank you for reading.