When leaving the Reserves For AD, when do I start getting paid?

"Soft orders" isn't a real thing. You have orders, and you have assignment instructions, but your assignment instructions will be more relevant later in your career. Right now you either have orders or you do not.

Exactly the same as every other military pay in the DOD, you get paid at the end the month. You report in early July. You probably won't inprocess early enough to be paid mid month July, you'll get paid end of month July, for the number of days you're on active duty

I went from E-4 Reserve to AD in '76. Back in the day, the commissioning was accompanied with orders with an effective date. I received an AD ID card that day too. Some things may have changed, but there are common mistakes the S-1 and financial types make that create problems you should keep an eye on. For me, they botched the O1E piece so I didn't get the pay based on 4 years. It took a BCNR correction and two years to fix and a Captain's Request Mast to direct the disbursing officer to cut me a check. The other thing can be transposition of the critical dates. The system said I wasn't in when I got my last reserve pay. Eventually the US Marshals showed up at my Mom's house looking for me. She sent them packing when they didn't believe I was on AD in Antarctica. Second time she did that as they were looking for me earlier as a draft dodger. Didn't want to believe I was on a tin can off 'Nam. Bottom line, you don't want mistakes creating gaps. Have the admin types walk you through the paperwork making sure you have proper accounting for all your time and proper stop/start dates. Also make sure you get the proper coding on your release that matches transfer to AD. You will be loaded into the AD pay system. That isn't instantaneous, so a lag can occur. If it does, you may be put off one pay cycle. Do the math on your LES to make sure you get everything you're entitled to. Read everything in the remarks section for accuracy. Good luck in your next phase of MIL service.