I would do some research on the yeast you are using. I think the dry yeast is usually gluten free and the liquid yeast may not be. Safale, saflager, Windsor, Nottingham dry yeasts are gluten free.
I plan on using oats and already purchased some for that purpose but have not got around to including it in a batch. Seems most of the posted recipes that use oats are people trying to achieve a dark beer like a stout. Are you cereal mashing your oats? I think like Buckwheat, if you don't boil it for 10 or so minutes before the regular mash then you just get too much starch in the wart.
For the batch with chestnuts, did you add amylase and pectinase? I followed the instructions on the Chestnut Trails site and my batch turned out tasting petty close to a couple of the Harvester brews. A lot of people really like the chestnut beer taste, but I realized after my batch and tasting Harvester, that I don't. Personal preference. Interested to hear what you think after your test batch.
For your GF Czech Pils, you may want to substitute some sorghum LME for part of the brown rice syrup. I think the rice syrup by itself does not have enough FAN and other stuff for proper fermentation. Then again, in the spirit of testing, go for it and see how it works out. If you find it to be a little thin and lacking, then substitute some LME for rice syrup, maybe 1 lb LME and 0.5 lb rice syrup.