Lacing is still offered by several custom makers and is rarely seen because it is expensive compared to stitching. El Paso Saddlery offers it and I think that rawhide whipped lacing is very attractive on a traditional holster.
Firstly, I recommend going to the Tandy website and watching ALL their free videos. You'll learn a lot just watching.
I would recommend a good awl and doing a saddle stitch, rather than lacing because it's easier to do. Good looking lacing takes practice but a straight stitch is easy. A stitching groover is recommended not only as a bed for your stitch but also to keep it straight and it provides protection for the thread. Make your stitch about 3/16" from the edge.
A good, sharp, diamond shaped awl is easy to use and unlike drilling, removes no material. The holes close up once completed and the stitching is much less obvious than even machine stitching.
You also want an overstitch wheel and set it to 5-6 stitches per inch. This is a cogged wheel that sets your stitch marks.
Saddle stitching needles are blunt and will not cut the thread as you do your stitching.
Most holsters are made from 8-9oz vegetable tanned leather. Marketed as "tooling leather" at Tandy, which is still a good source for leather, tools and supplies. As you get more involved, you'll probably want better tools like those from Barry King, BearMauls or Osborne but the Tandy stuff is plenty good enough to get started. Avoid the cheap chrome tanned leather because it does not work well, hold its shape or finish as nicely. Don't be afraid to dye your own work.
Glue is not "necessary" but most commercial and professional makers use it for a reason. It makes for a stronger seam, a much neater looking seam and it makes it much easier to stitch. As noted, it also keeps your edges held together and won't separate over time. A well done, glued and stitched seam is a thing of beauty all by itself.
Rivets are certainly not a sign of cheap leather. They are very useful for reinforcing stress points but shouldn't really be necessary on the mainseam of a holster. They are, however, quite often used on belt loops, small pouches, belts and bags. I prefer to use traditional #12 copper rivets instead of the modern plated variety.