Unfortunately there is no official way to get the InterRail reservations for SNCF trains online. However, there is a not 100% official way described here: rail.cc/en/interrail-train-reservation/tgv-sncf/42
Note - you should be able to use this way described by sidhamo2 in the link as well for the Lunéa trains, but only for a reclining seats.
To get your offical reservation (and this is what I recommend) you will have to go to a bigger rail station on mainland europe where you will get it at a staffed counter. That's possible at all SNCF stations but at many stations in other countries as well.
The price of the reservations is mentioned in the first post of this topic.
Regarding your route: That's certainly not possible in ten or even seven days - I'd recommend at least two weeks
for such a trip - but even then it probably wont be as fun as it could be. More stressful that you'd want it to be...
If you want further information on that please open a new post in the Travel routes section. Thanks.