I'd also look at doing the CPU upgrade first, with the A10 you're locked into a pretty poor gaming platform which would severely restrict a GTX1070.
A few points:
Check motherboard specs and prices carefully, more than a few 'H' motherboards are at a similar price to the less well known Z170 parts-The Asrock Z170 K4 for example-and they can offer some nice extra features for the future, even if you don't get a 'K' series CPU and don't plan on overclocking.
Like all the current Intel parts, Skylake likes fast memory, DDR4 3000 or 3200 is a good balance between performance and price but be sure the motherboard can support such fast memory.
If you have an OEM or System Builder license of Windows there's a chance you'll need to purchase another license for the new system, although Microsoft are (or were) quite nice about moving OEM licences over as long as you only install on the one system-if you have issues with activating your existing licence you can call Microsoft and activate over the 'phone. Either way it'll be a smart move to do a full reinstall as part of the upgrade.
Before you carry out the CPU/MB/RAM upgrade, go to the MB makers website and download the latest drivers to a flash drive, do the same for the graphics and monitor drivers, that way you'll not only be able to install them easily, but have the latest available drivers on your shiny new system.
Don't forget to save out those important files/game saves/photos/videos along with your internet favourites collection!