Hi chichilicious, welcome to JREF!
When asking for proof-reading from next time, please write what you intend to say in English as well, it will make it easier for others to give you offer you advice.
1. nihon ni itte irai nihon ga suki ni narimashita. dakara, ichi nen mae made, watashi wa nihon de benkyousurukoto ni shimashita.
Basically they are very good, except the part marked in red.
It means "until one year ago" which does not fit in the rest of the sentence. What did you want to say? If "one year ago", it should be "ichinen mae ni".
2. takusan iroirona koto wo keiken shitai.
This is good.
To unify the style (polite form) of the whole text, you might add "desu" after "shitai".
3. Australia to chigatte, nihon ha sugoku gamitsu de, soreni Australia yori, night life wa totemo ii desu.
Gamitsu??? In English?
4. nihon no ooki no apartment toshite yachin ga takasugiru soudesu.
Ookii itself is an adjective, you don't have to add "no".
Toshite means "as" or "for".
Nihon dewa ookii apaato wa yachin ga takasugiru soudesu.
(They say that in Japan the rent for a big apartment is too expensive.)
If you simply mean "very expensive", you can say "totemo takai" instead of "takasugiru" (too expensive).
5. tabun, nihon no daigakusei noyouni one room apartment wo tsukaimasu.
This is also good. Tsukaimasu (I'm going to use) is OK, you can also say karimasu (going to rent).
And also...can anyone help me with the sentence structure~
'i like 'something' as well as 'something' for example, if want to say -
i like japanese traditional culture, as well as their modern culture.
You can use "~mo, ~mo".
Watashi wa nihon no dentou bunka mo gendai no bunka mo sukidesu.
Watashi wa nihon no dentou bunka mo sukidesu shi, gendai no bunka mo suki desu.
Just for example.