I did the opposite of what you want to do about a year ago.
I routinely updated most all software on my PC using a USB drive stick for more than 5 years, before connecting my PC to the internet. But it will depend on what software you want to use as well. So what you want to do is possible for a large percentage of software.
True, but there’s also a lot less need to maintain the Windows system with all the latest patches, if it isn’t connected to the Internet.
I agree with Dragemester, in that life was much less worrisome without having the PC connected. After connecting I had to install and learn how to use a bundle of security programs I didn’t have without the connection and then there are my young daughters using the net. On-line and Off-line PCs have their pros and cons and it will depend on the primary use of your PC as to which route to take.