Fields visibility based on a dropdown number

I'd create a new module called Vehicles and relate it to Accounts. In creating the new Module I'd look at basing it on the Calls or Meetings Module if possible as the information you are largely setting up is date based (and possibly even recurring). You won't need to touch code, logic hooks etc just Module Builder/Loader and Studio. You can do this even if on Sugar Cloud. The benefits of a new module related to Accounts will be apparent very quickly rather than trying to add fields into the Accounts Module. 

Note only use the Module Builder to initiate the new Module. Do all the customisation, new fields etc in Studio. There is a SugarCRM best practice article on this. I didn't realise it once and had to recreate a module from scratch.

Well said Greg Barrass. Depending on the circumstances, I'd also recommend trying a Basic module if Andrea wanted to define all the fields and have more of a blank canvas, but this might be a personal preference.

Here is the article mentioned above too: https://support.sugarcrm.com/Knowledge_Base/Studio_and_Module_Builder/Best_Practices_When_Building_Custom_Modules/ 

Edit: these two articles may help as well in this circumstance:

• Sugar Logic Walkthrough - Next Call Due Date
• Capturing Records' Activity Counts Using Calculated Fields 

Thank you Alex, very helpful.

Thank you Alex, very helpful.