I've spent q few winters in the Long Term Visitor Areas in Quartzsite & Imperial Dam. I post a daily journal of the trip to & back, as well as the time spent in the south
I just arrived in Quartzsite today, but there are links at the top of the page to other trips. If you have a specific question, I'd be glad to answer it.
For your general questions - No reservations needed or can be made, at least for the BLM areas. There are a large number of RV parks in town - if you need utilities, reservations would be a good idea, although most have space except for the middle of January when The Big Tent Show is happening.
As to water, dumping & trash, if you stay at the LTVA, it is included - there is a dump station & water fill station at the La Posa South area. All areas have dumpsters & vault toilets. If you elect for a 14 day area, there are places in Quartzsite such as the Pit Stop where you can purchase water, dump, etc. You can drop trash at the Quartzsite transfer station a couple of miles north of town on AZ 95. They have limited hours, so check the schedule...