Where to keep the "good" tree and the "working"tree

(1) I'm new to FTM where I have the option of keeping trees both on my PC and online.

I'm a bit puzzled about where it is better to (1)keep the "main" (i.e. "good" tree) on my PC and keep the working tree online or to somehow keep both trees the same and somehow in synch.

The tree I imported into FTM was pretty much fully sourced, but now I'm working on new branches on the periphery - most of which at this point are speculative or at best low- to medium surety.

I'm looking for suggestions from those with more experience than I about whether it's better to keep one tree with speculative outer branches or to keep one fully sourced tree and one with the speculative branches.

I'd appreciate any suggestions.

(2) Is it possible in FTM to have the same person in two FTM trees? I ask this because another option I have is to keep the fully-sourced tree intact and start another tree with one of my source ancestors and build the speculative, low surety tree from that point in a new tree.

Thanks,

Wes