How likely is it that i can get a commission into a combat branch in the Army?

There are usually more infantry slots than people who want an infantry slot at OCS.

Needs of the army account for how many of each branch that have slot available, then there are the schools that have how many are wanting those slots, based on individuals choice of branch and qualifications, infantry is one of the most liberal as far as qualifications, and things like MI are much harder to get into. I was infantry enlisted, picked MI and SF for branches, and got infantry again. There's a good chance that if your already working in a skill, that you will get that same skill, but there is always the luck of the draw, they may see you have more potential, and put you into something that they think is a better fit for you, for the needs of the military. Good Luck.

Getting a combat arms branch if you request it should be a slam dunk. Not 100% certain, but very likely.

In my experience everyone I know got their first or second choice the vast majority getting their first choice

Work on a masters and do ROTC

It’s dependent on your ranking on the OML so the higher you are on there, will allow for you to get your first choice of branch assignment depending how many slots your class has for that particular branch.

If you want to go infantry, you can go infantry. The army will always need real leaders to do actual work. Remember: every mos is there to support the warfighters, and the warfighters wear infantry blue.