Most likely buying point to point - as far in advance - will be most economical.
You are right here, when the itinerary is fixed and you are sure about travel dates, then smartly bought in advance point-to-point tickets is an obvious choice.
Several point to points are too far to advance to book at this time.
In Europe railway companies for the most part start ticket sale 60-90 days in advance, however with some countries/connections this can be 120-180, but we definitely don't remember any case when it was >180 days. So in case you plan to travel all the way in September/October, you'll have to wait with ticket purchase. But meanwhile we advise you to try out earlier dates, look at the options we have in mind (see below), thus when the time comes you will already know what, where and how.
Let's just go leg by leg:
September 14th - Venice to Como S. Giovanni - 4 nights
Main idea here is to get discounted ticket for the part Venice-Milan (since you anyway will have to change trains in Milan). Discounted so-called "Super Economy" tickets for high-speed trains on this relation start from only 9 euro and can be easily purchased via
TrenItalia (Italian Railways) website. With part Milan to Como everything is very easy, because the route is served by regional (depart from Milan Central station) & suburban (depart from Milan Garibaldi station), 4,6 euro without any need to buy in advance and you there. But in case you want, TrenItalia website can also sell you through ticket Venice-Milan-Como, but watch out so that price for such ticket won't exceed 9+4,6=13,6 euro
September 18th - Como SG to Murren, Switzerland - 5 nights
Here it gets more complicated, both in travel matters (multiple train changes required) and in tariff nuances. Option A is to travel from Como S. Giovanni via Chiasso-Lugano-Luzern to Interlaken and then to Murren (takes around 6:30-7 hours and at best roughly 65 euro per person) or option B is to travel via western route, thus Domodossola-Brig-Spiez (this way is about an hour-30 minutes faster and you can count on 50 euro per person at best). Let us know which one is preferable and we'll try to explain in detail how to get the best price for it
September 23rd -Murren to Dijon Ville (Gare Sncf de Dijon Ville), France - 4 nights
Again quite a number of train changes will be required here. Cheaper option appears to be to travel via Basel (from
Swiss Railways website we were able to get tickets for as low as 65 CHF for the entire route), but also you can use route via Bern-Neuchatel, geographically it's a bit more straight forward, however it seems to be more expensive
September 27th - Dijon Ville to Paris - 7 nights
Here everything is relatively easy - multiple direct trains and tickets starting from only 15 euro.
French Railways ticket sale period is 90 days (SNCF also has low-fare calendar, so you can see distribution of discounted tickets depending on how in advance you purchase)
October 4th - Paris to Ghent - 3 nights
From Paris to Belgium best option is to start from
Thalys website. Tickets for direct high-speed train start from 29 euro, but if the schedule of this direct train doesn't suit your needs, then you can always travel by one of the many Thalyses (see same website) to Brussels (from 22 euro) and then catch local train to Ghent from there.
October 7th - Ghent to Amsterdam - 5 nights
No direct connection here, but you can easily reach Amsterdam with one change in Antwerpen. In terms of tickets everything is also relatively simple - with two tickets (Ghent-border (Roosendal) and Roosendal-Amsterdam you can get to Dutch capital for 35 euro and no in advance ticket purchase is needed. However you can also get discounted ticket for high-speed
Thalys on leg fro Antwerpen to Amsterdam, it will be slightly more expensive, but about an hour faster in total travel time