EDITED TO ADD: Hmmm, my quote buttons (and all other icons) aren't working ... please PM me suggestions for fixing.
Welcome to The 642 Club!
As for your questions:
1. I used to practice a lot with either Wallie World White Box 130 grain FMJ or Remington RNL 158 grain rounds. Now that I reload, I shoot either light 148 grain wadcutter loads or non +P 158 grain RNLs. Eventually I'll work up a +P recipee with 135 grain bullets to duplicate the Speer Gold Dot 135 grain +P hollowpoint, my chosen carry round (though I may switch to Buffalo Bore's non +P 158 grain round one day.)
2. Speer Gold Dot 135 grain +P jacketted hollowpoint. Recoil isn't much worse than standard pressure (to me anyway) and there is very little muzzle flash.
3. First, check several times to make sure the gun is unloaded and that there is NO ammo in sight.
I clean my 642 after every range trip. I also give it a 10 minute quick cleaning every few weeks to remove lint build up from pocket carrying it. The painted aluminum surfaces of the 642 can be sensitive to some solvents, so stay away from any foaming bore cleaner. Hoppes #9 and Breakfree CLP work great, especially if you spray the Breakfree down the bore and in the chambers and let it soak for 30 minutes.
I then scrub out the chambers and bore with a brass bore brush. I sometimes use a bore brush sized for 40 S&W to clean each chamber to remove any heavy residue buildup. The cylinder face (and ONLY the cylinder face) then gets scrubbed really good with Hoppes #9 using a stainless steel brush. I use a nylon brush everywhere else.
I also like to use a lead-away cloth on the cylinder face to remove the stubborn "ring around the charge holes".
Finally, I swab Hoppes soaked patches down the bore and chambers until they come out clean. I run a dry patch through them, then add just a tiny bit of cleaning oil to prevent corrosion. Wipe the whole gun down with a silicone rag and I'm done in 30 minutes.
4). I carry my 642 in a Robert Mika round-cut pocket holster. This setup works extremely well for me. Sometimes I use an el-cheapo Uncle Mikes IWB clip on holster that also works well. I have no experience with the Smart Carry, but have heard a lot of positive comments about them.
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For those concerned about needing more than the five shots of available in the x42, it is always a possibility. A very remote one, however. Most encounters involve exactly 0 shots fired. The best kind, for sure. Anything can happen, of course. But if we planned for "anything", we'd all be carrying AKs or Mossie 500 Tacticals around, at a bare minimum. I'd prefer an A-10 myself
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The best we can do is perform a threat assessment of where we live, work, and most frequent to determine the most realistic and likely threat and plan accordingly. I live in a very safe area. The most realistic threat I face are being jumped by 1 or 2 muggers or carjackers, typically armed with knives, or a maybe a gun. Anything worse than that, and I'd be moving. For me, the best carry option is the 642. It gets carried everywhere I legally can, it is simple to operate, lightweight, super reliable, quite accurate, points well, is very easy to draw, and possesses good stopping power with proper ammo. As for reloading, I do reasonably well using HKS speedloaders, though not as quick as my 1911 or even my 686+ (which I can actually load faster than the 1911, probably due to greater familiarity with the 686). I know, I probably won't need them. So it is a comfort thing I guess.
BTW, when at the range, I load my 642 and 686 exclusively with speedloaders. Sure, it's not as simple as dropping fresh rounds into the chamber, but I get lots of good practice time in.
I will carry my 1911 some in the winter. Not for the extra capacity (a whole 3 rounds) or slightly quicker reloads, but for the greater pointability and stability of the larger, heftier 1911 platform in my hands.
BTW, there's that saying about not bringing a knife to a gunfight, but facing even a single attacker at close range armed with a knife is definitely no joke. The 21 foot rule is a scary, but true thing.
Hopefully, no one here will ever have to deploy their 642 in for anything other than practice.