Its been ages since I changed my 1st Gen speakers so I dont know if you need the plastic adapters or not, but it was a straight nuts & bolt repair. No modifications were needed.
What speakers you want will depend on how good your stereo system is versus how much you want tp spend on them. A decent set of $50 speakers will def last you years.
I suggest you hit up crutchfields.com.
2005 5 cyl, Black on Black, 4 door
2016 Z71, Black, Long Box, 4 door
I did mine in my former 2005 Canyon ages ago as well...they are standard size and were a piece of cake to change out. Only thing I seem to recall is having to drill new mount holes as the new ones didn't line up with the old ones...but I'm not 100% sure of that though.