I would indeed choose some other word where all the cases are clearly distinguishable from each other. And which hopefully also supports obscure cases like instructive and
-tsi (I can't remember what it's called) and maybe some others).
Linguaphile wrote:3. (Accusative in Finnish. Genitive in Estonian?) I'll paint the house. Help me paint the house! = Ma värvin maja. Aidake mind maja värvida! (Should there be an "ära" here? Is "Aidake mul maja värvida" the same?)
I think you could call it accusative in Estonian too. At least it acts and behaves (almost) the same way as Finnish accusative - looking like genitive in some and nominative in other situations, according to a very specific set of rules. Even in your example, the first
maja "is" genitive, the second "is" nominative.
I think in Estonian, the notion of cases is usually avoided when referring to this construct. It's mostly referred to as "
täissihitis" (
total object?), as opposed to "
osasihitis" which is effectively partitive case.
Yes, if the case is not distinguishable then you should indeed use "helper words" like "
ära" (but could be also "
valmis", "
lõpuni", "
läbi", "
selgeks" and many others, depending on the sentence). Sometimes a "helper word" is even mandatory, when without it the meaning wouldn't be the same, or even the sentence wouldn't make much sense at all.
"
Aidake mul maja värvida!" is better. In my opinion "
Aidake mind maja värvida!" isn't very common, at least not in Standard Estonian. It even sounds a bit unnatural.
Also possible: "
Aidake mind maja värvimisel/värvimisega!"
(but in this case maja is genitive)Let's also cover these examples with another word - for example "
aed" (in the sense of
fence; the word
tara would be more correct in this case, but that's not a good word either, for these examples):
"Mulle ei meeldi selle
aia värv." - I don't like the color of this fence.
"Ma värvin
aeda." - I'm painting a/the fence.
"Ma värvin
aia ära." - I'll paint a/the fence.
(you can omit the ära if you use some other word, like punaseks for example)"Aidake mul
aed ära värvida!" - Help me paint a/the fence (completely)!
"Aidake mind
aia värvimisel/värvimisega!" - Help me with painting a/the fence!
Also possible: "Aidake mul aeda värvida!" - Help me do some painting of a/the fence! (the action doesn't have to have a definitive end result)Linguaphile wrote:8. (Adessive) See you at the house! = Näeme majas! (Better example for adessive: Näeme seal! [See you there! We'll see each other there!])
9. (Ablative in Finnish, but elative in Estonian) I walked from [one] house to another. = Ma kõndisin ühest majast teisesse. (Better example for allative: Ma kõndisin ühelt korruselt teisele [I walked from one floor to another]?)
10. (Allative in Finnish) When will you be arriving to [/at] the house? = Millal jõuate maja juurde? (Better example for allative: Paneme majale uued aknad [We're putting new windows on the house].)
Indeed, any of these are actually not the examples of the given cases in Estonian. For outer locative cases in case of
house, you could use giving/adding something (some feature or part) to a house, house having something (some feature or part) and taking(removing) something (some feature or part) away from a house, for example.
"Millal
maja juurde jõuate?" could be also "Millal
majani jõuate?" (terminative case).
Linguaphile wrote:11. (Essive) Are you using this shack as a house? = Kas te kasutate seda hütti majana? (Is hütt the right translation? Is kasutama the right verb in this context? Is essive even right or should it be something with nagu?)
Yes,
hütt sounds okay. Yes,
kasutama is the right verb. And yes, essive is the right case here.
I guess,
nagu should be also possible, but it doesn't sound very natural here.
Linguaphile wrote:12. (Translative) I'll turn it into a house. = Muudan selle majaks.
Again,
täissihitis. "Muudan seda majaks." would be
I am turning it into a house.
Linguaphile wrote:13. (Instructive - in Finnish. Genitive in Estonian if using järgi here is a reasonable translation. Although to be honest I'm a bit stumped with this one.) They passed on their message with(using) the houses they built. = (Nad) Levitavad oma sõnumit majade kaudu, mille nad (ise) ehitasid.
I think better would be "Nad levitavad oma sõnumit oma/enda ehitatud majade kaudu."
Or if it would just be "
they spread their message through houses", then "Nad levitavad oma sõnumit
majutsi."
Linguaphile wrote:15. (Comitative) He appears to be wealthy, with the numerous houses he has. =
Ta tundub olevat rikas nende paljude majadega, mille tal on. 
This is tricky. You can make many sentences with different meanings by fiddling with the order of words and cases used. For example:
"Ta tundub olevat rikas nende paljude majade järgi, mis tal on (/mida ta omab)."
(or "Nende paljude majade järgi, mis tal on, tundub ta olevat rikas.")"Kõikide oma majadega näib ta olevat rikas."
"Majade poolest on ta rikas."
etc...
I'll try to make sentences with a better word, as soon as I'll have time.