Do I have to stop using (& creating new) Google Classic recaptcha keys (v3?)

[TXWEBDESIGNER]

I've been plugging along for years creating my client's websites using google v2 / v3 recaptcha keys on their inquiry forms with no issue. They are very small business sites and they are nowhere near 10,000 assessments per month.  

I don't need all of the new features with the upgraded recaptcha and would prefer to stay with the V3 keys.  It looks like I can still get to the "legacy" console to create new keys.  Is this going away?  

I don't want to have to pay for enterprise level services so how can I stay under that and use the simple verification?  

I also don't fully understand what the new "Google Cloud Platform" field is and why I need to put a name there to create a new key.  

If I don't pay for enterprise and get above 10K assessments, what happens?  Spam could start getting through all forms after the 10K assessment level is hit every month?  The recaptcha won't display / work anymore?  

Thanks in advance!