There are a few options for using a dropper and seat pack if you want both, but they depend on dropper/frame/wheel clearance.
I have a few bits from appkit that i use for general riding/bikepacking/commuting.
I tend to use a front rack more now. and use rock straps to fix a dry bag down. Rigid forks so gives a solid base for heavy items, also very easy on off for commuting.
I have the tapered dry bag from alpkit, i’ve used it by itself but found it a pain if you need to be in it mid ride.
Id say get a handlebar set-up, frame bag and use your backpack to get you started. Then add from there.