Pachirisu is a great support with Bide, Nuzzle and Super Fang. Volt absorb will make beating Julia very easy while Pickup can get you some useful items.
Trubbish is not trash nor rubbish. Actually, it's one of the best poison pokemon in the early game. Learns Toxic Spikes before level 10, and Acid Spray at 12, as well as Toxic at level 36, making it a great status spreader and support in general. You can even poison the second and third Tangrowth with Toxic Spikes.
The mystery egg is also something you must take into account. At some point after the second gym (don't want to spoiler), you will be given an egg with a random pokemon. All the 18 possible pokemon in the mystery egg are good additions to your team.
These were my two cents, other people will recomend you more pokemom I guess.