How about the ruger gp 101 instead of the sp 101? I think you get 6 round cylinder in the gp 101 versus 5 for the sp 101.
Now on to your actual questions:
Question #1: As long as your handloads are jacketed bullets, then you should be fine with the stock glock barrel. The polygonal rifling of the glock barrels makes them prone to pressure spikes when non jacketed bullets are used.
Question #2: I've never shot a delta elite, but have shot the glock 20 quite a bit and it's a fantastic weapon. The one I shot was stock and honestly one of the more accurate service pistols I've shot. I was really impressed and I find glocks to be pretty average pistols in the accuracy department. The glock 20 has recoil similar to 45acp+p loads in my opinion.
Question #3: http://www.activeprogear.com/jogger_holster.html This seems to be the best option I found for jogging. It keeps the gun off your waist and therefore not tugging at shorts all the time.
I would like to throw out some info on the 10mm auto round. It's extremely versatile and has loadings up to 230 grains for bears and wilderness issues. It will push a 230gr bullet to higher speeds than even 45acp+p and you can go as light as 130gr. Actually you may be able to get bullets a little heavier or even a little lighter should you have a need. I think doubletap makes a bunch of 10mm loadings to choose from.