As far as typings go, I'd probably be rather tempted to make Embirch plain Grass-type as well, but I also really hate the idea of switching primary typings around. I can deal with Fire/Grass for it- it isn't a major deal for me, but it just doesn't look as Fire-reminiscent as the other two. The ideal solution, for me at least, is to make Pyroak Grass/Fire like Delta Nite mentioned, but I understand if sticking to its process more rigidly is preferred- and this is assuming more people agree on plain-Grass for it anyway!
tl;dr: not a big deal, do whatever
My critiques on your art will be honest! I'm not mean about it- or at least I don't think I am- but I won't lie to you. As a result, I'll always hide-tag my critiques (don't be nervous because it's hidden!). My praise, however, is also honest, and I'll never give one without the other.