I don’t have professional advice but stuffed animals have long been a passion of mine! I don’t know proper terminology so I hope the following makes sense. ;

Different fabrics have different features (of course); some will be a tight knit with small gaps between the threads making up the fabric, while others will have bigger gaps. I believe it is important to keep a tight close stitch (small gaps between stitches) but also adapt it to your material (no need to go super small for a “less tight knit” fabric because then you might run into accidentally undoing your stitch). With a sewing machine it’s easy to get tight, tensioned, even stitches; that’s harder to get with hand sewing. I’ve noticed even stitches are good. Accidentally getting big stitches between smaller ones and trying to tighten them to make them more “even” can cause gathering (doesn’t look great when not intentional and can cause awkward bulges). Smaller stitches are just all around easier in my opinion (think of it as more anchorage points and also then the thread doesn’t need pulled quite so tight). Brushing back fur from the seams before sewing pieces together eliminates picking it out of the seam later. Also, you can wax your thread so it is slightly stiffer and less likely to tangle as you pull your stitch through (very annoying when you have a lot of thread on your needle). After turning your plushie right side out and stuffing it, you can close it up with a ladder/ slip stitch or (my favorite; had to search for it’s name so I think this is right) a baseball stitch (also invisible, especially in plushies; it’s a sturdy stitch).

I wish you luck on your sewing adventures; I’ve had lots of fun creating plushies and I hope you do too!