I love Thangles, place the darker fabric on top then, when you open to PRESS you are always pressing to the dark fabric, saves a step that way.
Oh decrease the stitch length like in PP, makes removing the paper a snap.

When not using paper, as you draw the diagonal line, I use a roller chalk marker because it is too easy to stretch the fabric.

I always oversize.

Conquer 1/2 sqs and it will feel amazing - I know you can!!

what I worry about with this snowball type of block is getting that 1/4" seam allowance at the peak so I don't cut off the points

Ah, the mysteries of quilting and math. You measure carefully, cut carefully and press with care and you still end up with an off HST. I think the quilting goblins sneak in and cut some off when we're not looking. I use two square the exact same size and that seems to do the trick. The idea of making the HST larger and then cutting it to size may seem redundant, but if it works - do it.

I have made patterns where a half square triangle was used on a larger piece and the method used was to put the smaller square on one corner of the larger piece, (sometimes the larger piece was a square and sometimes a rectangle). In any case the outcome is a triangle. I found that to get the corner of the top piece to match the corner of the bottom piece after it was pressed into a triangle shape, I needed to stitch to the right (or closer to the corner side) of the line that is drawn to get them to compensate for what you lose in folding and pressing and come out more even. It also helps to use a finer thread like Aurifil 50 weight (LOVE that thread) so less is taken up in the sewing process.

Do you have problems with other seams mismatching?

If you have a machine that has a ppresser foot pressure adjustment feature, you couldd try lessenning the pressure.

Is it the upper or lower layer ( as you are sewing the pieces together) that ends up being " short"?

With Thangles, I found that I had to sew just on the inside of the line (on the seam allowance side) rather than stitching on the line. I guess it's basically the same as sewing a scant 1/4". Once I figured that out, my HSTs came out much better.

I recently tried Jenny Doan's method of putting two squares together, sewing 1/4 inch around the outside edge and then citing them apart on the diagonal. You wind up with 4 hst's and they were pretty accurate. Just a little trimming. There's a You-Tube tutorial online.

What I do is press corner squares in 1/2 and sew just to the right or left of fold depending on what side they are placed on the other square or rectangle. I did this to make the hearts on my irish chain but would work the same here

I bought Brenda Hennings Triangulations dvd and I can print off just about any size HST's I need. The resulting sqs are very precise with no irritating trimming needed. I will never do a HST's again without printing off stitching sheets that result in multiples of sqs. A +++ to Brenda H!!

I have found that by making the HST's slightly larger, like even 1/8", I mark the diagonal line, sew on either side, press, then trim to the correct measurement. It seems that no matter how careful I am, I usually wind up trimming to the correct size, some more than others, but it works for me. I would rather take the time to trim after sewing than to have pieces the wrong size, even by just a little bit.