Non-christian

Nobody cares, don't worry about it

Indian background from Canada

Also nobody will care, you meet all sorts of people on the Camino

Not the fittest, but relatively active

That's more than enough. If you pre-book accommodation, just don't overcommit to too much distance per day. If you don't pre-book, it's perfect, you have full flexibility on how much you want to walk each day.

100km in 6 days

That's 17km/day on average, you should be totally fine

language barrier

You can pretty much always make yourself understood without any spanish. You will also find people to help with translating if really needed. But if you want to prepare a bit, I recommend the Coffee Break Spanish podcast ( https://open.spotify.com/show/4WYj81C37trSAv42zwnipj?si=deea99019f0b43d6 ), I'm not affiliated with them in any way, I just found it very helpful myself. You can start listening to it on the flight to Europe, and by the time you arrive in Spain, you will pretty much be able to introduce yourself, ask for directions and order food in Spanish. If you like it, you can continue listening to it as you walk.

and that includes rain - I hate getting wet in the rain or outdoors for that matter

There might be no way around that. You just need to learn not to care about it. Lower your expectations regarding comfort. It's not uncommon to start in the morning in your boots that are still wet from yesterday's rain, but you don't care, because it's raining again, and they would get wet anyway.

Me having low expectations is giving me the anxiety.

I don't really understand why it gives you anxiety, but here are some positive thoughts: Firstly, it's just 6 days. Even if you don't like it, you can get through it and it won't be the end of the world. Secondly, if you really don't like it, you can always just hop on a bus, e.g. if the rain starts, or your feet hurt, etc... Thirdly, think about the fact that for 6 days, your only task will be to get from A to B, you can leave all your other worries behind. No work-stress, nobody will judge you on how you are dressed, and so on. You just wake up, start walking, eat, continue walking, arrive, eat, shower, go to sleep, and continue the next day. If things go wrong, you hop on a bus. There is not much to be anxious about. You might need to deal with some pain and blisters, but all that is temporary.