1: Esittely

Terve kaikki! Minun nimeni on Vill ja olen opiskellut suomea viikon. Suomen kieli on melko erilaista kuin englanti. Sanat ovat paljon pidempiä ja myös suomen sanasto on erilaista (I think both erilaista and erilainen can be used, just sounded better to me). Monet sanovat (Or 'Sanotaan,... which is in the passive tense), että suomi on liian vaikeaa, mutta minä osaan käsitellä sitä. (Not sure what you meant by the blue part. I'm also not going to touch your punctuation, I'm the last person you want to be giving advice on that.)

1. How do you express time that is ongoing? I'll try to put it simply. For days:

For a day: (yhden) päivän (ajan)

For X days: (Number in its basic form... oh, I'm also bad with the terms) päivää. You can also say it in the above way "... päivän ajan" but the problem is that the numbers are in a conjugated form. 1 becomes yhden, 2 kahden, 3 kolmen, 4 neljän, 5 viiden, 6 kuuden, 7 seitsemän, 8 kahdeksan, 9 yhdeksän and 10 kymmenen (so 7-10 don't change). For 10s it is the conjugated form of the amount of 10s + kymmenen + conjugated number of ones. E.g. 54 becomes viidenkymmenenneljän... ajan. For 100 it is sadan. If multiple hundreds, same rules apply.

For months:

For a month: (yhden) kuukauden (ajan)

For X months: X(basic form) kuukautta or X(conjugated) kuukauden ajan

Years:

For a year: (yhden) vuoden (ajan)

For X years: X(basic) vuotta or X(conjugated) vuoden ajan

I'll add these while I'm at it:

For a second: sekunnin

seconds: sekuntia or sekunnin

For a minute: minuutin

minutes: minuuttia or minuutin

For an hour: tunnin

hours: tuntia or tunnin (all three work like the previous examples)

The verb really dictates if it's still ongoing or not.

2. How do you express that something is different from something?

"Erilainen kuin + (noun in basic form)" or "Erilaista kuin + (noun in basic form)" Erilainen is used when the nouns are countable, erilaista if not. 'Erilaisia' if the nouns are in plural.

3. Are the suffix "-kin" and the word "myös" completely interchangeable, or is one more colloquial than the other? Perfectly interchangeable in my opinion. I think they are used pretty evenly, but in EXTREMELY colloquial speech, a contracted version of -kin, '-ki' is mostly used. Usually the personal noun is also in a shortened form.

  I thought about saying "Suomen sanastokin on erilainen." Would that have been all right?  Yes

Kiitos kun (te) luitte! (is that right? :P ) Personal pronouns can usually be omitted; the verb conjugates depending on the pronoun so it's apparent from there. Otherwise, yes.

Good job for your first try. Finnish has its own wonderful quirks, you'll have your hands full. :D

I hope this wasn't too confusing, I'm sure it's a lot to take in.

PS. Please don't take my advice on grammar as the absolute truth. I'm just a highschool student who almost failed Finnish. ;)