If you do not already own an MP, I would start with the phone you already have and see if the screen is big enough. I got the Wunderphone (search these forums) when I got my Mavic Pro a year or so ago and haven't needed anything larger. Although I had the intention of purchasing a tablet once I was used to the drone - never needed too. Not sure how available they will be since the US had its CFO locked up in Canada but I think the clarity of the screen in sunny conditions is better than my iPhone 6s plus (which I also use on occasion) and the screen size is
exactly the same. I also bought a few extra things right off the bat including a battery charger (
like this) which was my best purchase outside of the drone itself. I have the polar pro filter set (I made a comparison video
here) but honestly I do not use them much.
I was kinda in your shoes wanting to buy a whole bunch of stuff before I got the thing but if I did it again I would wait to see what I needed. I did get the fly more combo with the little DJI bag (which I think is awesome - holds the bird, 3 batts, extra props, controller, memory cards, etc.) and a backpack from Costco that I put the little bag in to carry everything (landing pad, charger, other stuff) including a gallon zip lock in it of stuff I have never touched - the OEM chargers, cords, not sure what else but it seems like a lot.
Take your time. Hopefully it will last a while but you could spend the whole $600, have a fly away experience so your DJI Care Refresh doesn't work (without the drone), and be out everything.... Never happened to me but lots of post about it especially with the
MP2.
Happy flying!