You may want to read some of the 30 or so pages on wholesaling in this forum. Just full of answers to all your questions above.
Number 1 and 2 are correct. Most contracts are assignable unless the seller adds an adendum or clause that says otherwise so you do not even need to add the or assigns. This automatically leads me to believe you are going to flip the deal and I as a seller may not want to sell to you. If yoy encounter this objection if using the and or assigns language you can tell them that you will be forming a partnership or LLC or something and need this to transfer the property at the closing. On a few I have flipped I told the seller that the buyer perhaps a potential partner I was showing the house to just offered me a sure profit and I took it.
How and when you get paid is negotiable. Some will pay up front or a portion at the contract assignment and some will want to pay all at closing. Some deals may be so large that you will want to do a double closing where the buyer will not know your profit.
Most title companies are familar with assignments.