What does it mean to fig a farm? We would use some different verb in English.
The -lima can be used both for noun (mkulima) and verb (like in this example)?
Yes. I think this is pretty common in Swahili. Putting m- on just about anything makes it a person (or at least alive.) Mkulima = person who farms/cultivates, mnyama = animal (literally living meat), Mtanzania = Tanzanian. Other prefixes can work like this, too, but they are a bit less predictable as to what it will mean. Ki- with a country/nation/similar makes a language (e.g. Kiswahili). U- with an adjective often makes a noun meaning that adjective's quality (e.g. "uzuri" beauty from "-zuri" beautiful). Swahili is cool because you can often reuse roots with different prefixes to get related words.
Please see dieprinzessin's comment above. Here's a dictionary entry to confirm it:
shamba nm ma- [li-/ya-]
1 farm, field, plot for cultivation; plantation, estate.
2 country side.