Hey there,
Ok, let's just dive into your questions.
1) The recommendation is seen, generally (not always, but generally) as the second to last or final component. Most will start with the resume or the application, move on to the second of the two, then move into the essays and recs. However, when they see it is generally irrelevant. All the top programs have a very robust process in place and reading it 2nd or 3rd or 4th doesn't skew your chances. They're very good about keeping it holistic.
2) The problem with this question is you're assuming a good rec and great rec follow the same strategy. That isn't the case. A good rec will merely reinforce the things admissions directors have already seen and provide little new information. A great recommendation is an integral part of your story that communicates and supports different key themes. I don't mean this as a plug but we've already written about this distinction on our blog and you can find that entry
here. So the difference between a good and great rec is significant. As for weight, that's too hard to nail down to a percentage. It can vary candidate to candidate based on the strength of their profile and application.
3) I cannot speak to the practices of any other firm. I can, however, speak for ours. We do not recommend or advocate our clients writing their own recommendations. We don't for a couple of reasons. For one, we are uncomfortable with the precedent this sets and the impact it has on the integrity of the process at a macro level. We have set our own boundaries and we don't cross them. Additionally, having an applicant write their own recommendations takes away the "character" that a recommender can provide. It becomes too similar and loses the different view points that are the whole point of a recommendation.
I understand your concern regarding the risk inherent in the recommendation process. I get it - you're pinning your hopes on a couple of recommendations! However, I think a lot of this comes down to your usage of "basic guidance". Yes, most do give basic guidance and they don't get in. A thoroughly prepped recommender, however, is one who has been given a clearly articulated strategy and story along with suggested themes of focus yet not too much direction that it loses the variability they can introduce. Variability isn't always a bad thing!
Let me know if you have any questions - I hope this helps!
Bhavik