With the QuickMapService plugin you can add lots of basemap including aerial imagery.
That being said most of online imagery are at low DPI as they are intended to be viewed on a screen, when printed the result is likely to be disappointing (that's also true for non imagery basemap). You may try to find some online service providing high resolution image (look for WMS service that let you request high DPI).
Another point to be avare of is the way QGIS request the base map tile on the print composer by getting higher zoom level tile to be able to produce the desired DPI output so what you see on screen is not what you will get to print.
Lastly, some provider limit the size of the image you can request/print (and 4 by 8 feet is for sure above the limit).Also don't forget to consider the licence of the data (printing for personal use is usually not a problem but there may be a size limit, for professional/commercial use there are usually more restriction).
For best result (and real control of your output) you should try to source and download a suitable imagery to work with (but high quality/high resolution and free are rarely seen together...)