I've been happily married 4 years. (We're lucky to have good examples - my parents have been married 38 years, his parents have been married 34 years.

)
You will fight. Every couple does. Heck, you'd probably disagree occasionally with
anyone you lived in close quarters with...family, friends, roommates, spouse.
How you fight is more important than
how often you fight. If you both "fight fair," the fact that you disagree or go through a rough patch is neither the end of the world nor the end of your marriage.
BTW - the suggestions to enjoy married life together a while before adding children to the mix are good ones. If by some chance fate has something different in mind for you, things can still work out well though. My husband and I have been married 4 years - our children are ages 3 and 2. I truly feel that our children have made our marriage stronger - knowing that we have this huge shared responsibility has solidified our sense of being a "team." No, I would not have intentionally
planned to have 2 children so early in our marriage, but that's what a strong marriage is about...adapting to whatever changes life throws your way.

(Note - it helps that we were 28 and 29 when we got married, so each of us had plenty of opportunity to do whatever we wanted throughout our twenties.

)