Ehm... sideburns are beard growing from the root of hair all the way down to cheeks. Ganryu and Heihachi, for example, have nice sideburns too. Pretty usual sight, I'd venture to say. They're called 'pulisongit' in Finnish, and I had to look from the dictionary what would they be called in English... hehe...
Describe? I suck at describing things, that's why I almost never write any fictions, I nearly always have to draw what's on my mind to have others understand what I'm saying. But heck, I'll give it a try.
Being at least originally Japanese, he has black hair, and judging from his current lifestyle and old-fashioned code of honor, I'd even venture to say it's long, black hair (not as long as mine, though. He keeps it short enough so it won't block his vision during the fights, unlike me and my hair :D). And since he was mechanized back in who knows when and updated more often than my computer, I say his appearance quit aging back then. That's why he looks way younger than that of his real age.
His scars vary from different kind of battle scars to a little scar across his lips (Kunimitsu gave it... she had long nails and perhaps Yoshimitsu was in a 'little too good mood'? :D). He got the scar that crosses his face about twenty years ago, defending his fiance from an attacker when she was pregnant.
(Now, before the flaming begins, may I say something? I would be rather dissappointed to find out Yoshimitsu has no offspring. I mean, come on! What has the guy been doing all his life? He can't be helping the poor 24/7, no one's sanity can take that, I tell you. Besides, if the sword runs in the family, Yoshimitsu, too, has to make sure he keeps up the tradition. Now I shall take cover under my table and wait for you to throw rotten Tekkens at me :D)
(Another note concerning the comic - even though the girl that calls Yoshimitsu "otosan" is named Kogamitsu, she by no means represents me. She was named Kogamitsu even before I joined the old YOT, so my nick is a ripoff from hers.)
Apart from the scars, Yoshi looks pretty ordinary (when Bryan came into the agency, he didn't recognize his own rival!). I imagined he had bright green eyes. You know... something like an aura from the sword itself.
Aside from that, Yoshimitsu has a great sense of humor. ("Well... I just thought he'd like his beer with some saliva.") That's his weapon against grief, and he uses it as efficiently as Tenshimitsu uses Yoshimitsu himself. His specialty is to make others feel better with humor, either joking about himself to about the cause of the grief.
Perhaps now you understand what I meant about I sucking at describing. I like to demonstrate things in practical situations or draw them out (I would make a terrible math teacher). But to dig up more characterizing of Yoshi, I would think he's not very picky about his title as the leader of the Clan. If some ninja - by mistake - calls him by his first name, he will think nothing of it. "So what? I call them by their first names as well."
Yoshimitsu in The Blood Ring is practically identical to Yoshimitsu in Rautanyrkki. A +100% more masculine, however, since it was me myself behind Yoshi's mask in the movie. I displayed my vision of Yoshi quite well in Rautanyrkki, even if I say it myself.
I hope this was at least little helpful... just throw a message at me, and I try and provide more answers, if you need.