Can I boot my mac from my old windows hard disk? Recently, my old windows computer broke down and I decided to purchase a Mac to replace it , and so far, it has been great!

I have thought about using bootcamp to install windows on the mac as well, as I need several windows specific programs for my college work. 

Rather than installing through bootcamp, I was wondering if it is possible for me to buy an external hard drive enclosure, place in my old windows hard disk (which has been reset and only contains a fresh windows 10 install) and boot my mac from that?

If possible, is there a way for me to get the Apple Windows Support Software separately in order to install all the required drivers on the windows disk?

Thanks
This is not possible.  Windows is not natively capable of being moved from machine to machine in that manner.  You could install a fresh copy of Windows on external media and copy all of your old files over.  Its time consuming but here is a link to some instructions regarding how you can accomplish this.
Is it possible to use Boot Camp with Windows 10 from an external HDD?