VM or dual boot?

I have one or two Windows keys that I can use to activate it. One copy is on my MacBook Air (using BootCamp). I'll be removing 7 from that today. The other copy was on my Acer Netbook, uninstalled it using "slmgr.vbs /upk". Got rid of the netbook.

If I use one of those keys, will I still be able to install the copy of 7 on another computer or will the key be tied to Windows 10 from now on?

If the key(s) you want to use are OEM keys, they can NOT be transferred to a different PC.
If a key is a RETAIL key, it can be transferred.

Are your keys OEM or RETAIL licenses ?

No, you can not use the W10 free upgrade offer and use the "W7 upgraded" license on any device at the same time you are using the "W10 free upgrade" OS/license.
The true COST of the free W10 upgrade offer is giving up a legitimate W7 or W8.x license.

You can revert back to the original W7 device/OS/license, if W10 doesn't work well for you, and you want to go back to W7.

The keys I used for the MacBook Air and the Acer netbook were both OEM copies. If I used this tutorial Product Key Number - Uninstall and Deactivate in Windows
can't I install the OEM copy on a different PC (or use the key to activate 10)?

I don't think you can do that according to the license agreement (EULA).
Here is a quote from the tutorial you used.

An OEM product key number is permanently tied to the motherboard of the computer it was first activated on. It can only be used to activate Windows on the exact same computer that it was first activated on.

A retail product key number can be used to activate Windows on any computer as long as the product key has been removed from any other computer first.

Source: Product Key Number - Uninstall and Deactivate in Windows

It may work for a while, but it may get blacklisted someday.
I'm pushing my knowledge and understanding now, i don't want to get banned for trying to help where what i say might be considered helping with piracy/hacking.

Wait for others to post that know more than i do :)

That old saying is true - there is no free lunch

I don't intend on piracy or hacking. Just seeing if it's possible (to use the OEM as activation).

I don't think you want to do anything illegal, and i didn't mean to imply that.
I'm just saying from what i understand and know, what you would like to do is not possible for free now.
You will need to buy a new license

So if I deactivate/uninstall an OEM copy of Windows, the disc/product key is no longer useful? Should I toss them or keep the disc for whatever reason?

So if I no longer have the computer/motherboard, the copy of Windows isn't any good?