Check out BEE Free, free online email editor to build responsive layout emails- https://beefree.io. It's helped us to streamline our workflow tremendously and the builder is very easy to use. If you like what they offer- it's only $10/mo to get the Pro subscription that allows you full access to their offerings- worth every penny for my team! Good luck.
This is a great question to consider. I have had this happen to me on several occasions as subscriber, and it can be confusing to suddenly be on a mailing list of a brand you have never heard of! I agree with Erin, my guess is that this is probably fine, but I am not a lawyer either. My primary concern would be communicating the change so that you can try to minimize the quantity of unsubscribes you get following this change. You will certainly see an uptick following the change, but having a strong strategy for communicating the upcoming change and maybe doing something with the sender name so it reads "New Company (formerly Old Company Name)"... A bit long but at least you've included both the familiar brand and the new brand together a few times to reinforce the message. Good luck!
There are two types of preheader text, "hidden" and "visible". The code you posted the snippet for is "hidden", meaning it will only show as the preview text in the email client, not in the email itself. If you want the preheader text visible in the email itself, just remove the style display:none from your code and it will display. You can test to make sure your hidden preheader text is showing by using the "Checklist" tool in Litmus. Hope this helps!
Before you drive yourself crazy troubleshooting your code, make sure you have upgraded to version 2.0 of the Marketo Design Studio. I had some odd things happening that I could not replicate outside of Marketo and after much troubleshooting, found that it was an issue that was resolved by upgrading to the newer version of the design studio. Good luck!