On the Roadmap tab there are only circa 20 fields I can add, do you know how I can add all of the other fields that are available such as 'Linked Issues' 'Description' and 'Summary.'
When adding a dependency it only gives me the option for 'Blocks' / 'Depends On' / 'Causes' / 'Relates To' - Expedia has loads of other linked issue types which we use, do you know how I add them?
I think the 1st thing you should do is talk with a Jira admin at the company, as not knowing which hosting platform makes it hard for the community to assist. Plus, a lot of it will depend on how the Jira admin/s have configured Advanced roadmaps.
They should be able to answer all the above questions.