My concern for your forearms was not the grip work itself more of the strongman stuff, with the sandbag you will be squeezing it so hard that it will wear on your forearms. But if you feel the need do it, because I have never been a fan of direct forearm work and never had any problems with grip on deadlift or anything else. I guess it works for some people.
Just my personal opinion, as a noob I do not really see a need for rear delt work but you can still do it, and on your Wednesday workout there is no back work. I really do not think you would have a problem doing another compound back movement like bodyweight pullups as far as overtraining goes.
Speed work could be done whenever you feel wore out or tired, or if you start to feel really slow. On your program you should do what you think is best and just feel out your body and watch your lifts. Keep a detailed journal and make notes about form, ease of the lift, progression and so on. The more notes you have the more you can critique your own program.
The best advice would be to get under the bar and try it!