A: Yes, it is sold with 5/8" bearings pre installed in each wheel, and has 3/4" bearings with it so you can switch them out as needed.
A: Steel. Good quality, with grease fitting. I'm happy with the purchase.
A: Yes they are metal.
A: Yes. I found them in the section where they sell landscaping parts & supplies.
A: It depends on the model of Gorilla Cart, but probably not. We recommend this tire for use with most Gorilla Carts that use a 13" tire: https://www.homedepot.com/p/Farm-and-Ranch-13-in-Pneumatic-Tire-4-Pack-FR1035/204405113 OR https://www.homedepot.com/p/GORILLA-CARTS-13-in-No-Flat-Replacement-Tire-for-Gorilla-Carts-2-Pack-GCT-13NF/303810061?keyword=gct-13nf&semanticToken=300300r00120000_1d40a15f23cd17a0a682123a04248a1d_1590179825753+300300r00120000+%3E++cnn%3A%7B14%3A1%7D+cnr%3A%7B7%3A0%7D+cnp%3A%7B10%3A0%7D+cnd%3A%7B4%3A0%7D+cne%3A%7B8%3A0%7D+cnb%3A%7B0%3A0%7D+cns%3A%7B5%3A0%7D+cnx%3A%7B3%3A0%7D+cnq%3A%7B0%3A0%7D+cnw%3A%7B0%3A0%7D+st%3A%7Bgct-13nf%7D%3Ast+oos%3A%7B1%3A1%7D+tgr%3A%7BNo+stage+info%7D+smf%3A%7Bca%2Cbr%7D%3Asmf+nf%3A%7B1%7D%3Anf+qu%3A%7Bgct-13nf%7D%3Aqu