You can apply 3vmonths early but as a visa is valid from the date of issue you will lose 3 months of it's validity. Timing is key to get the best outcome.
Yes unless you convert to the 65k monthly international transfer (income) for your extension from your second year or any year therafter (unless your Embassy does the income affidavit)
All Visa applications are now eVisa and getting a second passport will be a red flag to Immigration as both will be on his computer screen unless you get a second set of fingerprints too ;)
no, after submitting you print out the receipt and go the following day between 9 and 11 to pay then wait for the electronic approval, no appointment necessary