in the upper right you can change the profile in the main menu. i did both. kept the old game and started a new one. i don't mind regrinding the old challenges and stuff so for me it isn't a bother. plus with the difficulty options, which are new to me, i can mess around any way i wan't to. so easy mode and hard modes. it is all different flavors of fun.

I came back after the last major patch and just picked up where I left off before, you can still play lower tier areas if you want to get a feel for the game again but it didn't take long to get back into the swing of things.

you can just continue but i suggest looking into encyclopedia to double check if any evolutions requirements have been changed so u know what to look for

there is a chance some cards have been moved under a new unlockable so check your achievements and display blocked ones to see what you would rather do next