1. There is a field (eg bonus) which must be entered if user has selected 'Yes' option from a selection option ('Eligible').

Use a dependency group - see the module docs, using dependencies and dependency groups you can require a field to be filled in if a pre-requisite field is filled in, or if one of a group is filled in then all are required.

Getting digits only:

There is a Data::FormValidator::Filters module installed with the parent module. You can use a filer of ... digit!

field_filters => {
    cc_no => "digit"
},
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is an example form the docs for Data:FormValidator jdtoronto