Just see what is required for the 3 gun match such as .223 or .308 for long gun, .308 for 'he-man' only match and so forth. Red dot, scoped/no scopes, or iron only might be listed They might say to have a .40 or larger for pistol, just gotta see what is on the schedule. The uber tricked out AR's dont seem to place high, too much stuff gets in the way with the sling and switching to your secondary.
As far as pump gun go for it, half the people there will be with pumps. Dont get the shottie hung up due to short stroking it in an attempt to cycle it faster, or bang it back so hard that your next round does something like hang half way sideways out the ejection port. The jam adds way too much time.
One of the best ways to make up time is to be fast with your feet moving to the next station and try to remember your planned method of engagment, it sucks to blow through the course and see all this time added to your total because you forgot to engage a target, forgot to do a reload at a certain point, or not enough hits on certain targets like I have done
There is some kinda wording out there like 'slow is fast' or something, you pick up speed after doing more matches and practice. Your gonna save time on your sprint to the next station and having a quick good shot. You probably wont have the national masters grade type shooters show up at your match so just go and have fun with it.