What are the challenges when you do an upgrade from 7.5 to version 10 - (xforms is known). Do you have any recommendations?
There are a couple of things you should no about. First make sure you add the updateDataBaseSchema to episerver.framework section in config. Will help you when releasing to other environments that do not have the package manager console :)
There is also a lot of changes in the api that most likely will need to be rewritten: SiteDefinitionRepository and SiteDefinitionResolver have been replaced with ISiteDefinitionRepository and ISiteDefinitionResolver for instance. You will get errors and warnings when compiling. Most of them can actually be adressed before you upgrade to 10.
If you have moduls, thirdparty, make sure they support 10 as well. Some of them still do not support 10 sadly.
You will also need to migrate your Episerver site to UTC: https://tedgustaf.com/blog/2016/upgrade-to-episerver-10/