Translation:My experience from the trip was excellent.
To me, as a native English speaker, it sounds a little odd to say "my experience from the trip". I would say "my experience on the trip". I might say "the experience that I gained from the trip", but I would be at least as likely to say "the experience that I gained on the trip."
The meaning is the same, but grammatically is a completely different construct. It just so happens that yesterday this popped up: https://www.duolingo.com/comment/21835606.
In short, 'travel experience' is a phrase with a noun modifier (travel) that would be translated in Greek with an adjective: Η ταξιδιωτική μου εμπειρία ήταν άριστη. What we have in the suggested translation here is a word for word match, so why go beyond that if it works just as fine in the target language? :)
So in the light of "το πάρτι έκπληση" from your link, would it be possible to use "η εμπειρία ταξίδι" in the same way or do these "compound nouns" only occur in specific cases (as in English, where we can say "travel experience", but "trip experience" and "journey experience" would be understood but sound strange)?
No, το πάρτυ έκπληξη means the party that was/is a surprise. Something like ο άνθρωπος κεραυνός=the thunder man, for example. Η εμπειρία ταξίδι would mean something like "the experience that was a trip" making no sense. This kind of srtucture in Greek, compounds two nouns together and not a noun with an adjective, not even a noun with another noun that acts as adjective. The "travel experience" would be "Η ταξιδιωτική εμπειρία", an actual adjective is needed here.
Yes, there's a difference.
Trips and journeys are countable and refer to individual concrete instances of travelling, while travel is usually uncountable and refers more abstractly to the idea of travelling.
Sometimes you might use the plural, e.g. "How were your travels?" but it's still more abstract, at least for me -- it simply refers to all the travelling one has done recently. I don't think you could talk about "three travels", but "three trips" or "three journeys" are fine as those are specific instances.