Can I upgrade my computer after Win 10 install

I upgraded 2 tablets and 2 laptops from Win 7/8.1 to 10 and so far so good. Even the wife likes it (that is huge).
Now it's time to get Win10 onto my main/gaming computer (home build system).
There are some things, I can't seem to find the answers to.

What, how often and how much upgrading of the hardware can I do and keep Win10?

If I upgrade now and buy a new HDD later this year (SSD), can I then do a fresh install (I have made a DVD from the download). This means, the main drive with the upgraded Win 10 won't be in this computer anymore.
I regularly upgrade graphic cards, will this be a problem?
early next year I will do a complete rebuild, like skylake with new MB and DDR4 mem.

Once I go to the new chipset, I might be upgrading CPU, HDD, Graphic cards as needed, can I always use the same Win10 or do I need to buy a new version every time I do a transplant?
Thanks for any help.

well, it seems that I found some answers to my questions.
It looks like you can replace lots of hardware and if you get lost, MS will help you with the re-activation. However, this goes as far as the mother board. If you replace the mother board, you lose your operating system and will have to buy one again.
I hope more info will come out, once people actually have to go through some of these processes.
In my case, I'll make a decision some time later. not sure yet, if I want to buy win10 within the next 8 month.
I might wait until I upgraded the mother board on my main computer and then upgrade to win 10

I had to replace a MB on a Win 7 pc; a new key via telephone call to Microsoft & Internet connect, was $40. Win 7 was up & registered again after that.
Hopefully, that price has not increased.

me75006 said:

I had to replace a MB on a Win 7 pc; a new key via telephone call to Microsoft & Internet connect, was $40. Win 7 was up & registered again after that.
Hopefully, that price has not increased.

What? $40? I've done it multiple times with different versions of Windows and never had to pay a dime.

It was to microsoft. This was an OEM pc, and when the mb went, so did the key linked to the mb. new mb = new key.

Data said:

well, it seems that I found some answers to my questions.
It looks like you can replace lots of hardware and if you get lost, MS will help you with the re-activation. However, this goes as far as the mother board. If you replace the mother board, you lose your operating system and will have to buy one again.
I hope more info will come out, once people actually have to go through some of these processes.
In my case, I'll make a decision some time later. not sure yet, if I want to buy win10 within the next 8 month.
I might wait until I upgraded the mother board on my main computer and then upgrade to win 10

I believe that while the free upgrade offer exists (1 year from 29 July, 2015), if your qualifying OS (7 or 8) was a retail copy, you could install and activate it on new hardware, and upgrade that to 10 for free,

Whether MS will ever sell an upgrade version of 10, I don't know.