Let's give this a try then.
1. To allow people inserting our data into OSM, do we require to use ODbL?
Not necessarily. This is what OSM has to say on the topic:
We are only interested in 'free' data. We must be able to release the data with our OpenStreetMap License. Obviously we are allowed to use public domain data sources, of which there are quite a few, but beyond that, it gets more complicated.
So as long as your license is either very liberal (e.g. CC0) or compatible with the ODbL, it should be fine. Which brings us to your next question.
2. Is CC-BY-SA enough for OSM compatibility?
According to this discussion on the OSM wiki, I'm going to say no. The main problem seems to be the attribution requirement, although I don't quite understand why. However, when you license your data under both CC-BY-SA as well as ODbL, there should be no problem.
3. Else, what could be the advantage of CC-BY-SA in our case?
As you pointed out yourself, Creative Commons licenses are currently the best-known open licenses. A lot of time has gone into refining them over time, and since version 4.0 they are perfectly suited to cover data and not just content.
4. Does CC-BY-SA prevent OSM data to be inserted within our maps?
This is where things start to get interesting.
OSM state on their copyright page:
If you alter or build upon our data, you may distribute the result only under the same licence.
However, the ODbL states:
4.4 Share alike.
a. Any Derivative Database that You Publicly Use must be only under the terms of:
i. This License;
ii. A later version of this License similar in spirit to this License; or
iii. A compatible license.
So as long as CC-BY-SA 4.0 is deemed a "compatible license", all is well.
5. Is it correct to license XML file (SVG) under a Database license?
Well, I guess it depends. If your SVG is a creative work (such as a painting or drawing), then no. If it is just simple geometric shapes, then yes.
What about SVG file generated from OSM data?
If they are generated automatically, there's probably no creative process involved, so it should be fine to assume that a database license always fits.
This last question is actually a great example of one of the big advantages of CC-BY-SA 4.0: You simply don't have to care if your content is a database or a creative work, because the license covers both.
Disclaimer: I am not a lawyer, this is just my own personal assessment. I'm happy about any input and feedback :)