M.R.
My son Charlie stopped nursing at 4 months of age because I was not producing enough milk and he was under weight, so he started on formula and rice cereal at 4 months old. He loves food, but he does spit up a lot! Sometimes, it still amazes me how much he spits up :) Don't worry about the spit up, it is just what some babies do. I would definitely recommend giving your baby formula before the solids to ensure that he is getting enough to eat.
I would try to introduce some variety, pasta cooked really well and in small pieces can be fun. My son loves bananas, refried beans, cheese, whole milk yogurt, cheerios. They offer a variety of texture. Also, we only give Charlie diluted juice from a sippie cup, apparently, it is not good for babies to have juice from a bottle because it is bad for their teeth.
I would be confident that your son can gum food really well before I would introduce meat. Formula provides the baby with the vitamins and proteins he needs.
Hope that helps, feel free to email me ____@____.com