Currently we use the regular web signup form from CC but that form ads a Captcha when our subscribe rate reaches 50+ in a 24 hour period. IF we get an API key and use an API, is there the same sort of 50 subscriber limit in 24 hours? We've been with CC for 10 years and have 65,000 subscribers total. Having issues with people subscribing once we get past that 50 per day limit (at jongordon.com). Thanks.
While there are some limits to how many requests can be made in short periods of time to create contacts using the API, these limits are very high, and vastly exceed 50 per day, so I don't think you should run into any issues if you use our API with a custom signup form.
You can actually find a Custom Singup Form Generator with an integrated library that you can use to generate a custom formonce you have an API key. You will need to be able to install and run the form generator on your webhost or server configured with PHP. Documentation on installation, setup and use can also be found at the above link.
I hope this is helpful to you. Let me know if you have any specific questions about use of the API.