Simple clarification: preterito o imperfecto

Simple clarification: preterito o imperfecto
 

Vivía en el Ecuador --> I used to live in Ecuador.
cuando vivía en el Ecuador caminaba mucho cada dia

Viví en el Ecuador por casi 3 meses. --> I lived in Ecuador for almost 3 months

Despues de vivía en el Ecuador viví en el Perú por 4 meses.
After I lived in Ecuador I lived in Peru for 4 months.

Despues de vivía en el Ecuador vivía en el Perú

Corrections below:

By the way: I'd prefer "durante 4 meses", as none of the definitions of "por" in the dictionary talk about duration. However, I didn't correct it, because many native Spanish speakers don't find this use of the preposition strange at all. (I guess this might be because of English influence in Spanish)

Muchas gracias Angelica... así, tengo que usar el preterito siempre cuando doy un periodo de tiempo.. ¿si?

En la ultima frase... ¿puedo decir "Después de vivir en el Ecuador viví en el Perú"? Si el parte primera es en el imperfecto entonces el parte segunda debe ser en el preterito.. ¿cierto?

The answer for your first three questions is yes. :)

For your fourth question, I guess sometimes it is so, but I'm not sure that should be learnt as a rule... it's the situation what determines what tenses to use...

·Yo vivía en Ecuador cuando era niño, pero después mi familia se mudó a Perú.
("Vivía" and "era" agree because the speaker is speaking about a situation that used to be until something changed.)

·Yo viví en Ecuador cuando era niño.
(Limited duration --my childhood-- marks a preterite for "viví", but the ongoing situation was that I used to be a child.)

one clarification... I was taught to always use the imperfect of ser (era) when describing past characteristics of a person or a thing. Does this also apply to a description of a single event, for instance:

Juan: ¿Como te fue?
Yo: Fui al Mexico el fin de semana pasado, era muy divertido
[I went to Mexico the past weekend, it was a lot of fun]

[o fue muy divertido? o fue una experiencia muy divertido?]

Pienso que debo usar ERA ¿si?

Pero leí algunas cosas que un hablante nativo he escrito y el decía:
[But I read something a native speaker had written and he was saying]

Ya he vuelto del campo, estaba precioso

Why use estaba? It makes no sense. He is describing a characteristic of the countryside (el campo) so he should use SER not ESTAR. Then he is giving a description of a thing (the countryside) so he should use ERA.

"Era" would be needed if you're going to say that it was being fun, until something ended it.

And the person who wrote about the countryside was writing the right verb. The characteristic being described is perceived as temporary, as if it depended on the time when it was seen.

since you say "era" implies that the condition being described has ended and is no longer true when I say the following sentence how is it interpreted?

cuando era joven, era muy rico
[my understanding: when I was young, I used to be very rich] - I MAY or MAY NOT be rich at this point in my life so using era in this case is not giving me information that my condition of being rich has ended, correct?

descubrí que mi amigo me dejó 1000 dolares para mi cuando se murió, fui rico!
[I discovered that my friend left me 10000 dollars when he died, I was rich!]

I guess in the 2nd sentence I am using the perfect tense because I am describing an exact moment in time? I want to use ser instead of estar because I am describing a characterization of myself from that moment on rather than something transient, would my use be correct?