Hey @Jessica Gourdine rather than retype everything, here are a few threads that you may find useful. For questions on mailing frequency, what to say etc. I would recommend reading my response in this thread http://www.biggerpockets.com/forums/93/topics/102404-trying-new-marketing-routes
On determining ARV, check out my blog post here: http://www.biggerpockets.com/blogs/4218/blog_posts/29887-how-to-determine-arv
Equity is important because it allows the seller the ability to sell at a discount. You will likely need both equity and motivation for a given property to lend itself to a wholesale deal. If the seller is motivated, but there is no equity, there is not much you can do.
Buyer pays closing costs typically, you are assigning your contract. A contract is literally nothing more than a bundle of rights, you are assigning your rights in the contract to someone else. Unless you choose to double close, but I wouldn't worry about that in the beginning.
In regards as to what to say on the phone, I don't use scripts or anything of that nature. I am friendly and have a conversation with them, I don't interrogate them, try to beat them up on a price or sound like a robot reading line by line off some sheet. But I generally ask for property details, (the appraisal districts in my area are often incorrect on the # beds/baths etc). Ask them what the story is with the house, then sit back and listen. They will often reveal what their motivating factor(s) are lack thereof are. Once you have done several appointments and taken a decent amount of calls you will be able to figure out if the property has any potential fairly quickly.
Postcards can be long just like yellow letters it depends on your preference really. For instance a post card can be brief and to the point or it can be longer if you want a custom message and variable data. Personally I prefer short and to the point messages. I send the same message every time, the key is repeat mailings.
Furthermore the 70% "rule" is a guideline not a hard and fast rule. The all in % investors will buy it will vary and is hyper specific to your market and where your subject property is located and the exit strategy for the subject property. Here in TX landlords are commonly buying at 75-80%, in CA people are buying at 85%, thats at a national market level. Being hyper specific I could show you precise subdivisions in my area where the % number will vary. What, you need to get to know your market. Part of being able to do that is networking with buyers and looking at enough houses plus MLS access. This will come with time and persistence.
I would encourage you to know as much as you can before proceeding with wholesaling as there are many moving pieces. But you dont need to know absolutely everything. You can leverage others experience and expertise to help you on your journey by posting here on BP and gaining people on your team that will help you. For instance an escrow officer that is familiar with contract assignments. I still don't know all nuances of the title/escrow process, and the truth is I don't want to know all of it, I leverage my escrow officers experience.
Hope that helps