To build on what @Rob Beekmans said, you'll want to look at how they're deploying their desktops or RDSH servers. Are they using MCS or PVS? If they're using PVS, that might require an image rebuild since PVS is built for network boots. I'm not sure how common PVS is these days, but it might still be around in large scale deployments.
What other ecosystem tools are they using? Are they using the full Citrix stack for things like profile management and app layering? 3rd-party tools like FSLogix or Liquidware? Or is it a simple environment without any extra components?
What are their plans for Netscaler? Are they planning to keep it for load balancing other workloads, so you can use it with your UAGs and other Horizon components? Or do you need to find a new load balancer solution to support this environment?
And finally, I would recommend doing an actual performance assessment and use case validation. Make sure that you have good performance baselines in the existing Citrix environment so you can compare it to a post-deployment/migration Horizon environment, and you can use these numbers to validate that you have the right hardware or virtual machine sizing.
After seeing many load balancing questions on Reddit, I decided to write up an overview post on Horizon 8 Load Balancing. You can check out the post here: https://thevirtualhorizon.com/2024/06/17/omnissa-horizon-load-balancing-overview/
