Multiple blowouts in short time

Your first blowouts are not unexpected as the tires were old when you purchased the rig. GY Marathons have fallen out of favor over the years, and I don't think the GY Endurance makes your size. Sailun, although Chinese-made, has a stellar reputation. In fact, I've only heard of one failure, in multiple forums, and the reason was inconclusive. Lastly, there's no reason to replace bearings and hubs unless they already damaged. In some cases, its easier and cheaper to just replace the entire hub/race/bearing as a set.