I would highly recommend that you get a standoff holster. You need a little bit of space between your body and the gun. In SC it is all about speed and a half second means something.
As others have said you do not need mag pouches. 5 mags are good to have 6 if you like an extra for insurance.
OK I do not like to recommend anything, I'm not on sales retainer for any company in the firearms industry. Having said that....
Your standoff holster should be mounted on a stiff 2 pc competition belt. If you are looking for inexpensive (ha ha) the lest expensive is the shooters connection ultimate competition belt. From my perspective for production shooters it seems like the Red Hill Tactical competition holster is the most popular. I think you will need in addition to the holster and the belt a hanger to attach the holster to the belt. Look at something like the Ben Stoeger DOH Boss hanger. So consider calling shooters connection and discussing this with them. They are good people and understand the needs of competition shooters.
I have 2 full years in steel challenge and I'm an A shooter in Optical Sight Revolver and B in Iron Sight revolver, Open Rimfire Pistol and Open Rimfire rifle. Not an expert by any means. I shot my first match this past weekend in carry optics class using a production rig that has not seen much action. Mine is a DAA pro belt and the DAA PDR Pro II holster. I have about $140 in this rig. I do all of my revolver shooting with a race holster so using a production holster is a big difference. Why? Because you really have to lift the muzzle past the top of the holster before you can start swinging the gun up, which you can do much earlier with a race holster. For that reason I think the Red Hill holster is a better choice than the DAA because the Red Hill is cut lower allowing you to swing the gun earlier. But not enough for me to ditch the excellent DAA PDR holster.
You can use any post and notch sight for production. You cannot use a compensator but there is no power factor in steel challenge so as long as it cycles the slide use the softest load that is accurate. A failure to feed or jam is death in SCSA.
You are correct about practice X3. I use a shot timer with par time feature for dry fire. I start every dry fire session with about 25-30 draws to the first target. Your goal will better than 1.3 seconds from surrender position to first target so you absolutely must work towards getting a quick sight picture. Steel Challenge is great fun and really gets you to put a fine point on your skills. There are only 8 stages in SCSA but some guys live for this sport so competition is at times stiff. It looks easy and in theory it is but first time you shoot a match take a lot of ammo. It is not uncommon for a first time shooter to run out of ammo.
If I can be of any help fell free to ask!
ON EDIT.....
He can keep his gun in the bag/case just like the rimfire guys and uncase when the ro tells him to.
^^This is good advice from egd. Keep you gun in a case until it is your turn. Some guys keep theirs in holsters but I find this to be a giant pain the in * Competitors are required to paint the targets so keeping your gun in a case, keeps paint off it. Also, take a old pair of work gloves with you in case you want to help tear down after the match, the targets will be wet and messy.
One other thing. I don't know anything about the SR9 but I see it has a 4.2" barrel? Something a little longer would be better but for now I think it should work. My production gun, the one I turned into a carry optics gun for SCSA is a G17 so based on that I think your gun will be fine for now. As others have said it is a good idea to shoot a few matches to see where your interests are and what tackle you want.
In my humble opinion the lest expensive good mag pouches (for USPSA) are the ones made by Ghost. That is what I have but if I had it to do all over again I would spend a little more and get the DAA RACER mag pouches.