The thoroughness of driver installation with Windows 8.1 always blows me away. I've never had a problem with immediately upgrading/updating, you'll be fine (as long as you can connect to the internet).
Some drivers are cross-compatible (such as GPU drivers that work with 7, 8, and 8.1), however most are going to need to be re-installed. It's best to do a fresh install anyways just to ensure stability, so don't worry about getting them while in Windows 7.
As Don said, the OS install will do most of the driver work for you, however through my experience it often doesn't cover the GPU driver very well, and sometimes the chipset isn't covered. I did a fresh OS install just a few days ago and I had to download my own drivers.
TLDR; upgrade now and install the needed drivers in 8.1.