Redmine

Hello. I'm new at Ruby development and i'm having trouble changing (and reading) the source code for Redmine.
I'm trying to do two things, one of them is to make the custom fields in "New issue" dynamic. If the user selects the (custom) field "Project stage", he will be given a specific set options, for example, if he chooses the "Planning phase" option (in the project stage field), he will be only able to select PMO or analysis in the next field, which corresponds to Project stage. I'm trying to find the piece of code where the custom fields are shown to the user, so i can alter the code and make two fields "talk".
An easier way to explain what i'm trying to do is the common city/state fields, where you can only choose the city AFTER you choose the state, and depending on which state you choose, a specific set of options will be avaiable to you in the "Cities" field, it's exactly this what i'm trying to do in "New issue".

The other thing i'm trying to do is change the email sent to the users after a project is altered, created or removed, the link sent is localhost:3000 instead of the redmine website that i use.

As i said, i'm new at ruby, and the IDE i'm using doesn't help much ( i can't ctrl+click a variable to see where it came from, for example, and have to ctrl+f a LOT). It woul be very helpful if someone could tell me which part of the code i have to focus my attention on.