You have really only two choices of revolvers. Both are excellent. You have the Ruger GP-100 4.2" either the regular model of the more expensive Match Champion.. The Match Champion comes with a couple of nice to have features but both versions will work. The S&W 686 4.2" is your second option. I have both and there is not much sun light between either, Both will work, well. Excellent examples show up from time to time on the EE. Both are good value.
For Speedloaders Safariland 111' and Jet Loaders work well. I went with Jet loaders, others prefer the Safariland. Both work. You need four for IDPA.
Get a good belt. 1 3/4" is the maximum allowed. Revolvers are heavy.
Bladetech, Comp-Tac and Soley Canadian make good kydex holsters. Choose one.
You will need a concealment garment. While many go with a Hawaiian shirt (the godierr the better), light shirts can be difficult to manage and I would suggest a vest of some kind or a jacket that will cover your complete holster when standing in a scarecrow stance. Without some pracrtice a light shirt can get caught up in your gun in the draw and in holstering.
To compete in Canada only, we had an exemption for revolvers which allowed 5 & 6 inch guns to be shot in IDPA. This exemption was granted before Ruger introduced their GP-100 and Smith &Wesson followed suit with their 686 in a 4.2" version. For club level matches most clubs up here would not turn you away using a 5 or 6 inch revolver. For sanction matches though the restriction is 4.2" as it is in the US for all matches.
To the poster who commented on the 5" revolver. The rule is 4.25". I know you would like to play with your 6 Shot revolver from IPSC but the rule is the rule ad it has been debated long and hard for a change with no success.
To the OP go with the right equipment from the start. IDPA is great fun using a revolver. Once you have your equipment, practice your reloads and dry fire the heck out of the gun. Practice drawing from concealment. Bob Vogel has done a very good video on shooting IDPA and I would recommend it to you. With the new RB out in 2017 some of what he talks about is dated but his topics on shooting skills and shooting stages is spot on and will certainly move you along.
There is no significant rule changes for Revolver Division proposed in the 2017 RB so go to
www.idpa.com and download the existing RB and read up on Revolver Division. You will see where you can place your holster and speed loader pouches.
I hope you get into IDPA and play in Revolver Division. Great fun.
Take Care
Bob