Having done Reborn with a fire mono myself, I'd advise against focusing on bulkier types, as a lot aren't gettable till later in the game. iirc, Your next fire type after your starter is Vulpix, and you need to defeat a level 45 Klinklang to get it (when you're level 20 or so), and after that it's a Growlithe. Bulky types don't really come along for a while, and as said, Tepig is gettable later in the game anyway.
I started on an earlier version, So had 3 fire types before the second gym, but it will be a LONG time (5 Gyms at least) before you have a full team of 6 fire types, and none of them will be Bulky. (Have a look at my sig for my Reborn Fire teams-you'll need to scroll down).
When you get fire Types: Starter
Pansear is early, but sucky. Vulpix just before the 2nd gym is you get INSANELY lucky, or grind up to a point where you can beat Klingklang (by which point you could've beaten it normally anyway).
Litleo is at about the same time...but there are FAR better Fire Types.
Growlithe is right before the 3rd Gym, but you need to do a sidequest to find it.
You won't have a Fire Stone for a while yet anyway.
You can then Grab inferior fire types like Numel and Slugma once you reach the 6th Gym.
You'll get a Fire Stone next.
You're now at about the level to do the Gang questline, which nets you a Ponyta and a Houndour if you do it right.
You can grab an Eevee and turn it into a Flareon...if you're insane.
After that, no more for a while. Litwick and Cyndaquil come much later once you've beaten the 10th Gym.
After that, you have Magby at the 15th Gym.
Darumaka is got via Trading a Luvdisc, and Tepig via event.