Thanks for telling me your plan. If I don't comment on something, that means I like it and don't see any need to change it or give you more advice. :)
On the weekends I plan to put in 7-8 hours study
Do you mean 7-8 hours per day? Or 7-8 hours over two days? If the former, you will burn out and not make very good memories. Your brain can only learn so much in one day. If the latter (3-4 hours a day on non-work days), that's okay as long as you spread the time over 2 to 4 study sessions throughout the day and evening. That is, don't study for 4 hours straight or, again, you won't make very good memories and your study will be inefficient.
When doing end-of-chapter problem sets, don't do ALL of the problems at once. Do about half. Save the others to do later, for review. When you review, you'll also want to make problems and topics from different chapters or problem sets. The real test will never give you 5 fractions questions in a row - or even 5 FDP questions in a row.
You don't need to buy a separate book for DS, no. Each of our 5 quant strategy guides contains a strategies chapter and the first topic in each of those chapters is DS. Note that the first few pages of that lesson are similar across all 5 books, but after that, the material is different (so don't do only one strategy chapter in one book).
Other than that, I like your approach! When do you plan (roughly) to take practice tests?
In our course, we assign 3 practice tests over the length of 9 weeks (the time when people are learning all of the material in the books): at week 1, week 6, and week 9.
The first one is so that you know your strengths and weaknesses before you begin. That way, you can adjust your studies accordingly. The second one is to begin to get practice with timing and putting everything together under testing conditions. Don't be surprised if your score stays the same or even goes down on this test - that's quite common.
The third test is done after you finish your initial review of all of the books so that you can see what your strengths and weaknesses are at that point. You'll need to come up with a plan for what to review and how much to review it, and you'll base that on your specific weaknesses at that stage of the game.
That's about it - dive in and let us know how it's going!