May be I'm late, but for your info...
Sergei/Sergey"Sergey" - is more correct transliteration. But "Sergei" is OK too. Good choice.
Dmitri/DimitriCorrect transliteration is "Dmitriy"
Vladimir - another popular Russian name
Rostok"Rostok" isn't Russian name. "Rost
ik" is - diminutive form of "Rostislav". "rostok" in Russian literally mean "sprout".
Stasi- not a Russian name too

. There is name "Stas", short variant of "Stanislav".