I am sure this has been covered before but the search didn't turn up the threads I was hoping for.

Tessa (4 months) just won't quit jumping. She is getting better around me but she is impossible with people on the street. She immediately starts pulling towards them and then jumps like a jumping bean. I try to put her in a sit before the pulling and excitement starts but she will not keep her butt on the floor. I like the approach that she only gets to greet people when she's calm but we are never getting to that state. At all. For that very reason, it is especially impossible to socialize her with kids right now and I want to!

Jumping is also pretty bad in the kitchen (counter tops, before and after mealtime and anytime in-between). Reinforcing the sit with food works well while she is waiting for her meal but once mealtime's over, nothing will keep her off the counters.

I am new to the jumping breed ... we need help ...

Jumping is always a concern with a larger breed, espcially around kids and elderly.  I don't have the kid challenge at my house, but do have elderly parents.  So, I start mine out really early on no jumping.  There are several ways to handle this.  You are already using one which is making her sit prior to a greeting.  I know it is hard, but you have to be persistent and consistent.  Don't let up.  You are at a particularly challenging age with you pup too, so that makes it even harder and more important that you be consistent. You can also have the other folks turn their back to her when she starts her antics and then put her in the sit.  They can then turn around to greet her, but if she acts up have them immediately turn their back on her again.  Remember too you should be using a word like off (most people say down, but that typically means something else when we train dogs).  So, check you correction word to make sure it doesn't have a different meaning.  Then say no, off and as soon as she responds even if you are helping her tell her what a good dog she is (but only when she is where you want her to be). 

Finally, for counter surfing, be sure there aren't any rewards lurking on the counter.  I forgot one day and left a part of a sandwich on my desk and my 5 mos old found it.  Now he thinks there is always something good on the desk.  Then once you have cleaned off any rewards and worked with her a while, see how she does.  Again you have to be consistent.  Don't leave her alone in the kitchen where she can surf unobserved.  That is rewarding to her.  If you have to leave you can put empty soda cans in the area where she surfs.  The theory is she will hit them and they will scare her off.  I have never done this, but have a friend who says it works. 

You are right though to try to nip the jumping in the bud before it gets worse.  The bigger they get the harder it is to stop.