3-week June Itinerary: Galicia → Southern France → Switzerland → Veneto By Public Transport?

I’m planning a roughly 3-week June trip through Europe and would love advice from people who’ve done similar train/public transport routes.

The fixed points are visiting distant family in:

• Viveiro, Galicia
• Bassano del Grappa / Venice area

I’m also considering adding:

• Montélimar, France (friends)
• Zug, Switzerland (friends)

I’m flying from the US and am flexible about direction. Current thoughts are either:

• fly into northern Italy and work west to Spain/Portugal, or
• fly into Porto and start in Galicia.

I’m intentionally trying to keep this relatively low-stress rather than packing in nonstop sightseeing, so I’m trying to understand:

• which legs are pleasant/easy by train or bus,
• where flying makes more sense,
• how many nights people would realistically spend in each area,
• whether adding both France and Switzerland makes the itinerary feel too transit-heavy for 3 weeks.

Interests:

• food culture,
• markets,
• regional cooking,
• small producers/artisanal food,
• everyday local experiences more than major tourist checklists.

Questions:

1. Would you do this primarily by rail (or bus), or are there segments where flying saves a huge amount of stress/time?
2. Does this route make more sense east → west or west → east?
3. Best airport choices for Galicia? Porto vs Santiago vs elsewhere?
4. If you had to cut one stop to keep the pace relaxed, which would it be?
5. Any especially scenic or enjoyable train routes along this corridor?

I’ve started looking at Rome to Rio/Rail Europe/DB/Omio but would really appreciate firsthand experiences from people who’ve traveled through these regions.