That withdraw feature from the home loan sounds like a fantastic idea! Unfortunately, I don't know of anyone that does that here. Perhaps a line of credit on your house would be similar? I don't know, I'm not too familiar with this. Once you pay into a loan, you don't get it back. It's kinda a one-way deal here.
A lot of banks want an "Origination fee" which is usually 1% of the purchase price of the house. If you are not desperate, these fees are usually negotiable, provided you have the credit to back it up. In fact, all bank fees regarding a mortgage are negotiable if you are good enough at it. They can't make money if they don't get your business, but at the same time, with rates so low, they might HAVE to charge those fees to pay their people. Usually these fees are paid at closing, not to apply.
I don't know too much about them, but I have no idea WHY you would get an ARM when you can get a fixed 30-yr at 3.25% or a 15-yr. for even less. The rate isn't going to get much (if any) lower than that. Fixed rates are the most popular and probably the best deal you're gonna get IMHO.
As for credit, 690 should be sufficient. The better it is, the more likely you are to get the mortgage, but if you have the assets to back it up, you should be fine. They look at EVERYTHING, not just credit score nowadays. It's a real pain in the ass.