I think Coffer's book is the most popular and straightforward. It would be the first on I would recommend, especially with the DVD set. It does help to actually see someone experienced go through the process either on video or at a workshop.
Thge plain collodion USP is a mixture of guncotton dissolved in ether and ethanol. You still have to add the salts that will become light sensitive in the silver nitrate solution, and, additional thinning of the collodion is needed by adding ether and alcohol to the mix. Some people use grain alcohol (it needs to be ~190 proof ethanol to keep additional water out of the sensitized collodion) and some use denatured alcohol because of its low cost. It appears that additional ether may not actually be needed unless one is striving to do everything as period as possible.
I started to experiment with using a collodion thinned with only grain alcohol (omitting additional ether) and it seemed to work fairly well. My choice of salts confounded the experiment a bit, and I did not get very far with it this summer, but it looks promising and others report that salted collodions without additional ether work well for them.
Here's a full-plate ruby ambrotype from that experimental mix:
APUG's own Daniel Lin
This one was made on purple glass using sodium bromide and sodium iodide salts in the mix. Those salts seem to make the collodion set quicker and reduce the time available to work with the material compared to other salts (of pottassium, ammonia, cadmium, etc.).
I usually use my developer and then save and filter it. After it is filtered, I mix it half and half with fresh developer to actually get a bit more silver deposited on the plate (the first use strips some silver off the plate and puts it into the developer) and to shift the color more neutral.
A couple reasons for not dip/dunking the plate in collodion:
1) a thick coating is hard to properly clear
2) any solution on the back of the plate may migrate to the front and cause artifacts (e.g., "oysters") that most don't want in their plates. The rapid evaporation of ether and alcohol wicks everything to the front of the plate. This is also why points of contact are reduced between the plate and holder, and why dryplate holders won't work well for wetplate.
3) collodion and some of the salts are fairly expensive and coating the back would waste the materials for no benefit.