There's multiple sources on optimal commercial aircraft cruising altitudes being around 28,000 - 33,000 feet and higher for efficient fuel consumption.
http://www.fearofflyingphobia.com/flysohigh.html
In terms of military aircraft I am less knowledgeable but apparently the SU-24 was designed for lengthy low altitude cruising according to wiki and Sukhoi:
https://en.wikipedia.org/wiki/Sukhoi_Su-24
No optimal or min alt is given for cruising though.
In regards to the manpad your source claims that the min altitude that is safe to fly is 4.5km it seems. I was under the impression stingers had twice that range? Your source also quotes the Syrian army stating that the stingers where captured from their own forces so they should know roughly how many are in circulation or have been in circulation.
In terms of aircraft speed the SU24 won't stall at 700km/h. Whether it was flying at that speed I don't know as I am not sure what their minimum combat speed is for ground operations. 2.19km / 17 * 60 * 60 however places the plane at unusually low speeds.
I should point out though that the faster you go prior to a combat run the longer it takes to turn. The airport alone is apprx 50km away. Flying at 700km/h would result in getting back within 4 minutes and 14 seconds so its not a slow speed. No point going supersonic if you need to slow down and turn at a moments notice then line up with the target. The biggest evidence that we have that it wasn't going supersonic is that its wings weren't folded back.
http://www.dailymail.co.uk/news/article-3331558/Turkey-shoots-fighter-jet-Syrian-border-Local-media-footage-flaming-plane-crashing-trees.html
You said 2.19km but Turks said "a depth of 1.36 miles and 1.15 miles in length". Basically, it means that they moved on 1.15 miles inside, which represented a "depth" of 1.36 miles from the southern border. 1.15 miles = 1.8 kilometers. So this is even slower and corresponds, as I said, to roughly 300 km/h. "Unusally slow" would be more than a euphemism.
As you said, the SU-24 was designed for low altitude cruising, however you forgot to mention this: "
at supersonic speeds [...] in order to traverse enemy air defenses."
So I'm not sure that the unfolded wings prove anything. At which speed do they usually unfold? Moreover, the plane was apparently getting up, and not down, so it's very well possible that the pilots unfolded after the hit as they tried to keep flying.
As for the stingers, apparently you saw the "range" which is different from the altitude. The max altitude of the stinger is 3500 meters.
See there:
http://www.armyrecognition.com/united_states_american_missile_system_vehicle_uk/stinger_fim-92_fim-92a_man_portable_air_defense_missile_system_manpads_technical_data_sheet_picture.htmlOtherwise the MH17 could have been destroyed by any Russian manpad.
Does it matter whether a Stinger would have been able to destroy a fighter jet, or not? Fact is, that it was shot down by the Turkish Airforce.
We were talking about stingers and manpads in general because you can fly at low altitudes when you know that there is no risk. At the beginning of the war the Syrians were fighting at very low altitude with their Albatros and were even bombing with helicopters. But now they just can't. So if we want to determine the altitude, and consequently the speed, we must discuss this risk.
