"The girl often plays with the dog."
Translation:Flickan leker ofta med hunden.
It's not strictly ungrammatical, but it's not really an idiomatic construction to put the ofta after the prepositional phrase.
Not really – spelar is used for playing instruments or playing rule-based games but leker is for free games.
It's the v2 rule - if you don't put the verb in second position, it'll take a crowbar and budge its way there regardless. :)