strosfann;
Good morning to you sir, I hope that you're getting weather you can live with in your section of Texas and you're well.
There's been a whole bunch of good ideas thrown out here, hopefully some of them are useable and useful to you.
After reading the replies a few other thoughts have bumped into my head so here goes.
When I'm ice fishing I have a chunk of 2" Styrofoam SM to put my feet on. I've laminated both sides with that plastic waferboard from political signs. It's amazing how much warmer my feet stay when on that and not on the ice.
Scarfs and even balaclava type headgear is comparatively thin, easy to pack and goes on and off as needed easily.
As 257Bob says, don't have the layers too tight, like our houses it's the air between the insulation doing the job.
Taking all these clothes into account - you might need to shorten your length of pull on your rifle. Many purpose built Canadian prairie rifles have really short lengths of pull and the unknowing might think it's because they're all my size - 5'6" on a tall day - but that's not the case. Try shooting the rifle going with you while you have 5 or 6 layers of clothes on.
By the way, that's not an exaggeration - typically here in late season where it's only -15° to - 28°C on top I run a merino base layer, then my "lucky" cotton camo, then an ancient Rocky fleece shirt, next a light down vest, next a hoodie and last a heavy wool sweater. I'll have a heavy vest and if it's really cold a camo Gortex parka strapped to the pack some days too.
So for sure, the length of pull or perhaps placement of the ocular lens at very least is something to consider.
My fellow Canuck from the land of my birth and first 20 years castnblast is spot on regarding mitts. I run a heavy wool liner mitten under welding mitts. Disposable hand warmers last about 3 hours ice fishing for me - regardless of what the package says.
Lastly I use a 3/4" foam pad to sit on these days, the ones they sell in the sporting goods stores for hunting that are camo on one side usually. Honestly I just discovered them a couple seasons back and they've added hours to how long I can comfortably sit.
Hope that all made sense and was useful.
Best of luck on the hunt regardless and all the best until then as well.
Dwayne
