Well, it’s certainly a good thing that your bulbasaur is used to pokémon that would naturally harm him. I have no doubt that his relationships between these pokémon will only continue to grow. Should you be worried at all that either of them would harm him, it’s thoughtful but not necessary. So long as your noibat and growlithe are in full control of their abilities (which they should be if they’re tame), they should pose no threat against the new addition to their family.
That having been said, as part-plants, remember that bulbasaur need warm, sunny places to lounge and clean water, just as any other plant pokémon does. He will also need at least six hours in direct sunlight to avoid wilting, so ensure you have a place by an eastern- or western-facing window for him to lounge. (However, it’s better if he can lounge outside as much as possible.) If you can, give him a flat stone to perch on. The warmth from the stone’s surface can be relaxing to the reptilian half of his body. Additionally, keep him warm during the winter months; never let him outside without his growlithe partner, as the cold can freeze his bulb.
Other than that, the reptilian part of his body eats insects or very small pieces of meat in addition to kibble. He can eat the same things as your growlithe, but be sure that they’re much smaller, as bulbasaur don’t have teeth quite as sharp as canine pokémon.
It’s also perfectly normal for your bulbasaur’s skin to be on the dry side, but if it appears cracked, that may be cause for concern. Look out for any signs of lethargy (refusing to eat or sun, for example) and take your bulbasaur to the nearest pokémon center if you see these signs in combination.
Beyond that, bulbasaur are among the easiest pokémon to take care of. That’s why they’re frequently given out as starters. (Or … sold to children by less reputable dealers, not to reference anything in particular.) So long as you give your bulbasaur a steady supply of sunlight, water, and food, your bulbasaur will generally be very happy. You don’t really need to give it many toys, either, although some bulbasaur trainers give it balloons, install hooks high on walls, or generally provide their bulbasaur with distractions that it can play with using its vines. However, given the fact that it has companions who would have toys of their own, your bulbasaur may be content enough to play with his companions. The only thing to keep in mind is that a happy bulbasaur may vocalize frequently, especially at night or when it’s close to evolution. It’s best that you let it. It should only be a cause of concern if your bulbasaur vocalizes too loudly (that is, loudly enough to disrupt neighbors) or not at all.
Also, be warned when it learns Sleep Powder, Stun Spore, or Poison Powder. While bulbasaur are conservative about spraying powders or spores (their go-to defense mechanism is Vine Whip, followed by Razor Leaf), they will use Sleep Powder if they feel easily excitable pokémon such as growlithe are getting too excited for their liking. Other than that, it may be best to watch out for Razor Leaf and Vine Whip as well, although in general, bulbasaur are very difficult to startle into using their attacks.
Best of luck, anonymous, and congratulations on your new bulbasaur!
The Pokédex According to Bill 