I'm getting my first Bass now my problem is that I'm not sure what sort of wattage I need ! I've heard I'll need from 30W too 350W !? How much do I NEED to be heard over my friends Lead Guitar (I'm not worrying about drums yet).
depends on where you're going to be playing and what the people you're playing with have. if your just playing in your room and stuff then 30W will be fine. but if youre planning on cranking it a bit or playing at smaller venues then go with 100W or something. I wouldn't say you need anything above 200W though unless you plan on playing a big club or something.

on another note: I have a 100W acoustic bass amp and have played gigs in small clubs and backyards and never had to crank it up past about half way or so.
If you're only playing with one guitarist you should be fine with 30W as long as he's not on a really loud amp. Once you start playing smaller gigs then you might want to go up to 100-200+W.
So that with good courage we say, “The Lord is my helper. I will not fear. What can man do to me?”

-Hebrews 13:6
With just one guitarist (and as long as he's not cranking the volume on a Mesa halfstack or something), 30 watts will be fine. If your gigging with a full band, its debatable, but the general consensus is around 200W-300W for anything but a small venue.

Searchbar it, there was just recently a good debate on necessary wattage
Composite Aficionado

Spector and Markbass
Remember, it is always ok to ask the guitarist to turn down, if it's just the two of you. But yeah, I use 100W for small gigs with drums and two guitars, and they yell at me if I crank it.
I have:
Acoustic B200H+B115 cab, Schecter Stiletto Custom 4, Rondo Fretless, Boss EQ-7.

Some men just want to watch the world burn. And they work at Behringer.
I gig a lot. A lot. With a lot of different type bands.

I would never want to go anywhere with anything less than 200w. Even to practice with my regular band (trio of bass drums and guitar)