Hi there. Others might be able to advise on the other stuff but for food, the supermarkets don't offer a great deal really. Bagged mixed leaf salad (without beetroot, carrot, red peppers) is about the only thing and romaine lettuce and little gems are the best of the lettuces. Some wild rocket in moderation and bagged lamb's lettuce maybe. The trouble with lettuce is there's no real nutrients in it, it's about 95% water. The red lettuce (radicchio is it?) that you get in bagged salads is supposedly slightly better for nutrients. Obviously it depends where you live but there's still plenty weeds about, sowthistle, dandelion (in moderation like rocket) plantain. When mine are outside they have access to weeds growing out there but I also supplement with pellets which are called Pretty Pets Large Tortoise Pellets only available in UK from Ebay as they are imported. There are other types in the shops which mine have never eaten and I've tried them all. T-Rex Dry formula was one they did but they are no longer available.
*Another thing to remember is that the 'safe to eat/not safe to eat' articles are not an exact science. A lot of stuff may not be safe to eat for humans and some animals but tortoises are reptiles. There was an article I once read about Horsfields which said they ate plants that were toxic to other animals and because the other animals couldn't eat them there were loads of them for the tortoises.
As for growing indoors, you can plant the seeds and they will sprout but become all straggly due to lack of natural light and natural outdoor conditions. The Tortoise Table has lots of information on foods
https://www.thetortoisetable.org.uk/
At this time of year you might find your new pet won't fancy eating much and will probably slow down because in the wild they would be doing that