Is my guinea pig cage too small? (details)?

Yes. That is far too tiny for a guinea pig. I also don't recommend leaving it stuffed animals for company, guinea pigs chew on everything and fabric/cotton fluff isnt exactly good for their systems. Its "cute" I guess, but the health risks override the entertainment benefits. Stick to edible scenery, Im sure your pig will prefer that anyway. I dont suggest using fabric bedding either, they make different varieties, if you dont like the mulch chip styled stuff ask someone at a local pet store about different varieties and if youre still unsatisfied you can always use newspaper (just take out the slicks) but I suspect your pig will like it less.