Just a possible improvements firstly (if there's no comment it's just a correction)
planeando mis vacaciones de otoño próxima -> planeando lo que voy a hacer para mis próximas vacaciones, en las cuales me van a acompañar mis primas... - the way you use 'vacaciones' makes it seems like school break, otoño is masculine so 'próxima' is incorrect but you don't need to mention autumn anyway, 'en las cuales' is fancy and gets you marks; it matches the noun it describes, e.g. "Mi dormitorio (masc. sing.), en el cual tengo tres sillas,"
Buscamos para -> estamos buscando / buscamos
...culturas diferentes, para aprender..., para hacer... -> culturas diferentes, además de aprender..., hacer..., y... - para is repeated too much and not needed, and 'además de' is a nice connective
pensamos que podríamos -> pensamos que podemos / pensábamos que podríamos - you must either use two presents, or imperfect with conditional
To answer your question, I think this is A/A* level from this snippet alone - good range of tenses and vocabulary. Nice structure overall. I advise you use the subjunctive once or twice in the essay to really impress the examiner, even the imperfect subjunctive, and a couple compound phrases, e.g. "Inicialmente, habíamos planeado hacer.... pero al fin no fue posible porque..." (we had initially planned to do.... but in the end it wasn't possible because...), or double infinitive like "Me encanta poder hacer" (I love being able to do).