Dell Inspiron 15R HDD questions

Hi all, I have a Dell Inspiron 15R (SE I think) laptop that has the 32gb mSATA card in it from factory.

Today my main HDD crashed on me and wont load windows. I know for sure 100% it is the HDD as it had been getting more and more errors since installing Windows 10 and now boot sector is bad and wont boot into windows at all. 

Since the HDD crashed I am thinking of buying a new HDD and a bigger mSATA drive that will be able to run the windows full operating system (not just a rapid start device) and some commonly used programs.

However I do recall a few years ago when talking to a technician him saying something along the lines of my operating system is tied to the serial numbers of the HDD and mSATA. You can change one out but not the other to still keep a copy of windows. 

I do not have any boot disks or recovery disks. The ones I made originally when I got the computer do not work, all my recovery files left me when windows 10 decided to update itself.

So I have a couple of questions:

1. Because my main HDD crashed does this mean I would have to buy retail version of Windows? or would I still have windows if I only change out the HDD and not the mSATA ?

2. If I have to buy the operating system again retail, I will definitely change the mSATA to a larger one. Is there any restriction in size? I was thinking 120/250GB one.

Thank you for your time. Tim