I'm starting a piece using 7/8 time. I've never used it before, only 4/4, 2/4, 3/4, 6/8, and 3/8. And help for the rythim/not going completely crazy?

The first time I played in that time signature (Undertow by Mackey) we learned to count it in eighth notes. Two sets of two and a set of three. That's counted 1-2 1-2 1-2-3. The other way I know of is just counting to three and holding the three a little longer. One two threeee. Lol. It's inaccurate but easy.

Look at your beat groupings. Likely the beams connecting the notes will be grouped one of three common possible ways.

1 and 2 and 3 and a (ONE-two ONE-two ONE-two-three)
1 and a 2 and 3 and (ONE-two-three ONE-two ONE-two)
1 and 2 and a 3 and (ONE-two ONE-two-three ONE-two)

Likewise, many conductors will often conduct these in three. In same order:

One-Two-Threeeeee. One-Two-Threeeeee.
Onnneee-two-three. Onnneee-two-three.
One-Twooooo-three. One-Twooooo-three.

Any clearer? Basically there are just seven 8th notes in a measure and we're putting a mild accenting on the first of each beam group. The most accent is of course still on beat one, no matter what (unless there are accents/articulations that indicate otherwise).

Thank you! That really helped!