just started my journey and i have lvl 10 chikorita any suggestion which Pokemon to get in the starting of the game?

Then your rival got a the fire pokemon, so you should atleast get a poliwag since it is good against your rival and when, IF you use water stone for fully evolve it becomes a good fighter type too.
a flying type would be good for the 2nd gym so a pidgey or spearow.
if you not have beaten first gym which is in VIolet city, go down to the grassy area at route 32 and get a mareep which is electrical and good against first gym.

and maybe a gastly from the sprout tower?:)

for me that always is a good beginning, then I change my team a little bit later in the game, when i need better pokemons

i suggest maybe a gyrados because of it's very high attack and the fact that it will counter Typhlosion. i also recommend you don't use more than 3 pokes so you don't end up under-leveled by the time you reach the elite 4

Get the Pokemon you like best. If you train them enough, they'll beat pretty much anyone regardless of type. Mareep and Wooper are my favorites.

I actually reached to the 8th gym with nothing other than a Pidgey and Vulpix. One of my 2 favs.

God knows where my totodile is at..

Seconded on Lapras (Union Cave basement on Fridays, southernmost area, only after you get Surf so you'll need something else like a Wooper to stick it on). Also, recommend you grab a Fire type (Vulpix or Growlithe south of Ecruteak, and Magmar in the Burned Tower) and an Electric type (Mareep south of Violet).

it depends on how many pokemon u want on ur team. usually people have 4-5 pokes on their team to have room for an hm slave or soemtimes six if they dont mind switching out pokemon sometimes. So I'll give u a good idea for the 3 most likely situations.
So Chikorita is weak to Fire, so go with Wooper. Chikorita is also weak to flying so Mareep would help. And Chikorita is weak to Poison so Drowzee can help and Wooper can also pitch in. Thats an ideal 4 pokemon team for Chikorita. If ur interested in a 5th, try Sudowoodo to cover Chikorita and Drowzee's weaknesses to Bug. And if you want a 6th pokemon, you may want Vulpix/Growlithe to cover the grass weakness Wooper and Sudowoodo share. Furthermore, it also helps since Mareep's electric moves and Chikorita's grass moves aren;t very effective on grass pokemon.