conditional formatting for form input, when user enters wrong input

1. does anyone know of a good post for conditional formatting when entering information on a form? based on a boolean value for example? 

yes, formatting rule can be based on boolean value (eg. Yes/No check box control). 

in fact, rule's formula has always evalaute to boolean true/false value. if it doesn't, it's automatically converted to boolean value.

but the question is very general, I'm not sure what's exactly you'd like to implement

2. is there a way to calculate and display the length of a field as a user is entering the information?

yes, it's possible.

easiest way to implement is to use calcu;ated value control, as you did. it evaluates immediatelly once (any of) a field the formula depends on is changed (efectivelly: when the value is changed and control lost focus). I think this might be sufficient in your scenario.

if you'd like to recalculate on each keystroke, you'd need to write a javascript for that.

see eg. https://community.nintex.com/t5/Community-Blogs/Nintex-Forms-how-to-limit-maximum-length-of-input-field-during/ba-p/80315

along with visual 'alarm' to notify something is not inputted as expected, do not forget to implement a validation (validation rule, control's validation...) . formatting rule nor any notification made with javascript do nor prevent submitting incorrect input.

However when I go into the form, 

I've a feeling you wanted to continue with this....

so please don't think i've not appreciated the time taken to answer my question

no problem :smileyhappy:

and also does Preview mode show live calcs?

yes, preview performs calculations for calculated value controls, formatting and validation rules.

... as far as these do not depend on a value that's only available in runtime (eg. list fields value)