First things first, the Vortex 285 has not been produced by ImmersionRC for close to 5 years. It is considered a 'legacy product', and will no longer receive firmware updates.
Some replacement parts are available from resellers ( has a good selection of most ImmersionRC vortex parts, when they are still available). 

Solutions to Frequently Asked Questions are listed here:

1) Where can I find the manual?

The latest manual (v1.0) is available from the IRC website here

2) What is the latest firmware release?

The latest firmware release, (with betaflight 3.1.7) is available here.
As mentioned above, this will be the last release for this legacy product. 

3) Where can I download the Windows device drivers?

Drivers are available for windows only, from here

4) Where are the tools to update firmware?

The latest configurator (ImmersionRC Tools) can be downloaded from here.

5) What receivers are compatible with the Vortex?

The Vortex 285 was shipped during a time when SBus was still a common receiver protocol, and SRXL-2 was the latest and greatest from Spektrum.
ImmersionRC's Ghost radio system can be bound in SBus mode, and is 100% compatible with the Vortex 285.
Recent open source alternatives, such as ELRS, are CRSF-only, and cannot be used with the Vortex family.