there are loads of things you should consider- just cos its gona be a bit of hard work doesn't mean you should switch off to the idea- all Alevels are hard!!
anyway- paticularly with russian, you have a good chanc of doing really well, its not as common as french/german/spanish, chances are it'll be a small class, and universities love any level of a language like russian because russian linguists are in demand. lus it sounds impressive lol
yes, languages, unlike a subject like history, are about consolidating your knowledge and practising but you will be surprised by how quickly you pick it up even if it seems complicated, with russian if you've done gcse you'v covered most things with tenses and the alphabet haven't you??
then again its your future -only choose it if you are confident in your decision