by retroflex I meant the 2nd meaning, bubblehead - in English, some people pronounce their 'r's by kind of pushing the tip of their tongue against the palate and bunching it up, and others do it by retroflexing it, and touching the palate further back with the bottom side of the tip. It's funny since you wouldn't really know this unless you were a linguist and actually studied how sounds are made. Though there's really not much difference in sound, and it's kind of an unfair comparison with japanese r/l almost. I pronounce it both ways, actually, not sure why or when.
Now, as for 'v' in japanese - no, a speaker of (only) Japanese wouldn't be able to pronounce it since it's not in their standard set of consonants. You have to realize that there is no language that has ALL the possible sounds. I don't think there's even one that has even half of them used. The japanese tend to replace 'v' with a 'b', because it's closest one they have phonetically.
You would do the same with, for example, a Russian 'ы' - since english doesn't have a high back unrounded vowel, you would replace it with the closest thing and make it sound like an 'i' when trying to pronounce a word from Russian that has it (usually written as 'y', while it actually sounds like... try pronouncing a 'u' without rounding your lips

)
Another example is the Japanese 'f' which is actually different phonetically from the english 'f'. Whereas in English, you make an 'f' by blowing air between your bottom lip and top row of teeth, Japanese pronounce it by blowing air between BOTH lips in a similar manner. Since english doesn't have that sound, and japanese doesn't have the english 'f', both tend to pronounce the other's 'f' like their own, which ends up sounding kind of inaccurate.
As for the rolling R - it's a tricky one, I haven't studied it much as far as Japanese. I think STANDARD japanese (tokyo dialect) uses the liquid r/l, but when you hear all those characters from Osaka, you do get that rolling R trill occasionally (like the famous 'KORRRRRRAAAA!!!')
Anyway, that's more academics for you. Shows you what I've been doing these past 2 years

The Birds are using humanity in order to throw something terrifying at this green pig. And then what happens to us all later, that’s simply not important to them…