I'm honestly not entirely sure what your actual confusion is here.
First, ir and estar are completely different, and I can't think of any situation that they would be easily confused in beginning Spanish1. In your example, you have
- El viaje fue interesante.
But the present tense form of this is
Es comes from ser (to be), not ir (to go) nor estar (the other to be).
Your question title (as opposed to the content of it), makes me think that you are more interested in the difference between ir and ser, rather than ir and estar:
IR SER ESTAR
fui fuimos fui fuimos estuve estuvimos
fuiste fuistes fuiste fuistes estuviste estuvisteis
fue fueron fue fueron estuvo estuvieron
It's actually generally quite clear which one is meant. Consider the many different present tense uses of ser: soy alabameño, eres interesante, es cierto, etc. Ser is followed by either a noun or an adjective.2
On the other hand, consider how ir is used in the present: voy al teatro, vas por la oficina, vamos hacia el centro. It is almost always followed by a preposition indicating motion. In the rare case that it appears to be followed by an adjective, it should most normally be interpreted as an adverb as in ¿Cómo va? Va excelente(mente). 3
In fact, for most sentences, the uses are so distinct it's simply not possible to have an incorrect interpretation. Consider the above examples in present tense. If we swap the verbs, we get horrendous sounding sentence that don't make much sense: *voy alabameño, *va cierto, *eres por la oficina, *somos al teatro. You can generally use that as a guide to decide which interpretation you need.
The difference between era/fue is a distinction not of verbs, but of aspect (preterite vs imperfect) and bested suited to a different question.
1. At best, perhaps something like estoy de luto and voy de luto could cause confusion for learners. But that is because de luto is a phrase that can function as much as an adjective as an adverb. Other phrases can introduce similar difficulties if it's not immediately evident how they function in the sentence .
2. For learners of Spanish, I've found it's easier to simply say that ser always has a noun after it. Comparing estoy feliz vs. soy feliz, estar can never have interposed noun: *estoy una persona feliz. For ser, that noun is implied, as soy feliz and soy una persona feliz are identical in meaning. Effectively, when used with ser, an adjective is necessarily nominalized.
3. This is technically not an adjective, but rather, an unmarked adverb. In Spanish it actually uses the neuter form of the adjective. This is identical to the masculine in modern Spanish (except for demonstratives), but can be demonstrated by analogy in Asturian or cases in Spanish where otherwise femenine/plural would be needed but a masculine-singular-looking form is used: ¿Cómo vamos? Vamos excelente. (not excelentes, which has a different meaning).