I don't put many miles on my Mustang EB. I do an oil change once a year when the oil change light comes on. I've been using Amsoil Signature Series oil and either Wix or Amsoil filter. Yes, fill with filter is 6 quarts.
I changed my MT transmission at about 10-12k miles. I used the recommended Ford fluid and the 4 ounce bottle of Ford additive for the carbon synchros. It seems to shift much smoother with the additive.
First 1000 miles for break-in according to Ford.
https://www.fordservicecontent.com/Ford_Content/vdirsnet/OwnerManual/Home/Content?countryCode=USA&languageCode=EN&Uid=G2383639&ProcUid=G2177436&div=f&variantid=9122&vFilteringEnabled=False&userMarket=USA&buildtype=web