A:AnswerYes it is compatible with the MacBook Pro and iPhone 6. Your software drives the size it can print, but yes the printer can print larger content on 8.5x11" (letter) sized paper.
A:AnswerYes, you can load paper into the paper tray that is on the backside of this printer. Here is a quick video on how to load the paper: https://www.youtube.com/watch?v=FmYqDek63TU
A:AnswerYes, this printer comes with HP ePrint. You can set up the printer with HP ePrint, which essentially gives the printer an email address. As long as your printer is connected to the network, then you can email with or without the attached documents and photos and they will automatically print. Here are more details: https://support.hp.com/us-en/document/c03721293
A:AnswerYes, as long as your Mac is running MacOS Sierra v10.12 (previously OS X), MacOS High Sierra v10.13, MacOS Mojave v10.14 or MacOS Catalina v10.15.
A:AnswerYes, you can use basic printing paper in this Deskjet 2755. This link will take you to the HP everyday copy and multipurpose paper. https://www.bestbuy.com/site/hp-everyday-copy-multipurpose-paper/3412676.p?skuId=3412676