Øvelse gjør mester! :) (The Norwegian equivalent to "practice makes perfect". Literally "practice makes [you a] master)

(Den første oppføringen*) Første innføring/den første innføringen/den første innføringa  - Smart Mus disguise (?? I don't quite understand what you mean by that)

Hei ! Jeg heter Mateusz. Jeg bor i Polen i liten landsby. Jeg er 28 år gammel. Jeg vil skrive mange** mye fordi ønsker jeg*** jeg ønsker å practiserepraktisere Norsknorsk****.
Jeg har det bra i dag, jeg har en fint***** dag.
Jeg håper du også har en fint dag.
Ok Har det bra. Vi skrives

*"oppføring" is a word associated with theatre - "Les Misérables hadde sin første oppføring i Frankrike". The meaning is usually "performance" - "Les Misérables was performed for the first time in France".

** "Mange" means "many". The word you want here is "mye", which means "much".

***It is correct that after many complementisers, there is an inversement of the subject and the verb. Generally, this happens when the complementiser takes the role as something more than just introducing a subordinate clause. For example: "Igår kom jeg tidlig. Nå kommer jeg sent" (Yesterday I arrived early. Now I'm arriving late.). "Når drar du imorgen /i morgen?" (When do you leave tomorrow?). But "fordi", "ettersom", "siden" and many more conjunctions and subjunctions do not trigger this inversement process.
**** Only the country is written with a capital first letter. In English, all languages and nationalities are written with capital letters (like "English", "French", "Egyptian" etc.). This is not the case in Norwegian ("engelsk", "fransk", "egyptisk" --> BUT "England", "Frankrike" and "Egypt" because these are the names of the countries. They are "names", and names are written with a capital letter.)

***** "fint" is the neuter form of the adjective "fin". As "dag" is a masculine noun, the adjective which modifies it must be in agreement with the noun. "En fin dag" - ("dag" is a masculine noun), but "et fint eple" (a nice apple - "apple" is a neuter noun")