Let me jump in on a few points again;
Not a big problem, because the aircraft itself is cheap and you shouldn't lease aircraft longer than 7.5 years, so an expensive D-Check is nothing you have to do.
This is a big problem. In my eyes it's the most biggest problem of USSR aircraft. Due to it's high range and slower speed you can't do a daily schedule on most longer flights, so it will hurt your airline and your financial statistic when you deliver Aircraft #1 in January, Aircraft #2 in March, Aircraft #3 in July and so on. In the last Jet Age it took me an average of 15 month to get me 7 aircraft for a good schedule.
And there isn't a single Tu-114 on the used market you can get to fill up those gaps.
DC-8 has the advantage of offering a good and big production line. It loses a bit the first years to the 707, especially the 707-320 (but I noticed sami increased the range of the DC-8-31, nice thing), however, you can later replace them without any problem with DC-8-61/63, while Tu-114 must be replaced completely.
The "other aircraft production line may be filled" argument isn't one I count. If you have a decent long-term strategy you will get your slots. And if not you can make every aircraft to a "good alternative".