J.R.
Hi I am a mother of two a girl who is 6 and boy that is three, I have always started my children on solids very slowly.There digestive systems are very weak and new and has to get use to new food and to digest it propaly. My pediatrician tld me to start of with roots, like carrots swaeet potatoes and potatoes, and to feed one food example, carrots for a couple of days 2-3 days then try sweet potatoes for 2-3 days, and then alternate them for 2-3 days,and then move on.
This way if he is allergic to something you would easily be able to pin point it. If you just give him everything all at once his body is going to reject it because it is new and strange that is probably why he is vomiting, Protein always comes last at least wait until 10-11 months , because that is very hard to digest.
Good luck remember there is no need to rush food he has his whole life left to eat.