We are never given a clear-cut answer to that, though presumably someone knows it. As far as I remember, about a dozen clones have been identified, though I had to look some of their names up.
The list you provided in your question includes every clone that plays a significant role in the show, except for two (one of which you'll meet in a couple of episodes):
Rachel Duncan, who has always been self-aware and works for the "bad guys".
Tony Sawicki, a trans-gender clone seen in Season 2.
Some that you've seen already, but probably didn't catch their names, are the ones found in Katja's briefcase, which Sarah recovers from her hotel room. The briefcase contains evidence of Helena's earlier victims, and includes three of the European clones you mentioned, all of whom are dead.
We also see at least one more clone's medical records in Season 2.
However, there are a number of incidents that happen in the show which, I feel, are intended to give the impression that there are way more clones than we'll ever meet. Two such cases (I think these are early Season 1, so you've either seen them or will soon):
- At one point, Delphine reads off the list of clones that Cosima knows about to Dr. Leekie, and she names everyone that we know; Leekie's behavior implies that he's got a long list of those names in his head, and is just ticking them off as she says them.
- We know of at least 4 people Helena has killed; however, the way her handler talks about her, I got the impression that her body count is much higher.
Finally, as a HUGE spoiler:
There is also the next-generation clone, Charlotte, and the male Project Castor clones, both of whom are revealed at the end of Season 2.