Federated = Email. Different email providers (Gmail, Microsoft, iCloud, etc.) can all communicate with each other freely and using the same protocol.
Defederated = No longer federated.
Not federated = Your company’s internal Teams/Slack/whatever messaging system. Even tho they theoretically could communicate without other messengers and/or people outside of the company, they typically don’t do they’re just their own little bubble.
Lemmy is federated, Facebook is not.
If you mean for processing, I’m not sure what would be difficult about one credit card processor over another. The 4 major networks do charge different fees to merchants, so if that’s your primary concern, Visa and MasterCard will typically be the cheapest, but that’s more-so up to your clients and what cards they use.
If you mean for purchasing, I would think the only additional expense to you would be any applicable annual fees (which many business cards do have). There are plenty of business-oriented cards that don’t have annual fees tho, like the Amex Blue Business Cash card. If you value customer service over everything, I’ve personally found Chase to have some of the best customer service from a bank/credit card provider, but many major banks will be competitive in that regard.
If you mean more on the front-end / client-facing side, there are numerous services such as Square and Shopify that can simplify and streamline things, but that of course comes at an additional cost.
Hopefully that helps, otherwise if you can provide some more specific info on what you’re looking for, I or others might be able to provide better help/advice.