Muting with pick & left hand bad habbits

[FraGMenT]

First things first, congratz for the forum! it has been already usefull to me just by reading some topics.
I'm new at the forum and this is my first topic. Thanks you all for keeping the forum alive.

I've been learning the bass basis for two years now. I had to learn everything alone and from the roots.
I've learned some music theory, ear training, reading tabs, and practice (practice the less bth :f).

So there are a few things that disturb me.

Left Hand:
· When I play I realize I tend to move the thumb of the left hand until it gets horizontal (perpendicular to the other fingers). Is that a bad habbit? should I try to fix it or is it ok?
· I read around here that you should still be able to play even without the thumb touching the bass, but I realized I can't do that.
· About the other fingers... I don't "hammer" the strings with them usually. I tend to press them with the fingertips instead. How bad is that?

Any tips / tricks? ^^

The other question is about playing with pick. I've learned to play with fingers and I have some problems to mute the notes while playing with pick.
I began to use the pick two weeks ago and I had serious problems to mute the notes at first. Now I usually mute the notes now with the right hand's little finger but I guess there might be some easier way to mute them.

I've taken a look just in case those questions were answered somewhere in the forum and didn't find anything, but if the have already been answered I'd be happy just with the links to the posts ^^'

Thanks in advance and sorry for my bad english
Greetings form Spain! ^^'