what would you recommend ? Surface Pro or Book 2 for Animate

I would suggest you do NOT get a Surface anything. Especially if you want to use it with Animate. In order to get it to work with pressure sensitivity you have to do a bit of tweaking

Re: Adobe CS6 Brush tool DOESN'T WORK with Surface Pro 4. Photoshop works fine. Using latest wintab driver.

and while it apparently works it doesn't work for everyone so I don't know if you should risk it. I would suggest instead a Wacom Mobile Studio Pro

Wacom MobileStudio Pro | Wacom

Or if that's too pricey I bought a used Cintiq Companion off of eBay which works beautifully. I mean to each his own but I've wanted a Surface Book for a long time because they're sweet looking but I can't bring myself to do it with all the troubles Microsoft has had with them.

Simple: Surface Book 2 comes with dedicated graphics: either a GTX1050 or GTX 1060, while the Surface Pro has Intel graphics only - which are terrible for graphics work.

256GB SSD will suffice, although you will have to get an external drive to move projects to when you are done. Flash animations aren't that big - raw performance is more important to animate. 16GB RAM minimum is advised for intensive graphics work.

i5 will suffice. BUT! The Surface Book 2 configuration with an i5 doesn't have the GTX1050 option. You will need to get the i7 in that case.

that's the minimum ram and that ssd is very small.

if you're not adding must to your computer and doing nothing complex/large in animate, that will work, but i wouldn't use that.