First and foremost, welcome.
I would suggest taking a look around this website. It has a lot of information that would answer some of your questions. Also do a search in threads discussed in the past. I'm sure all your questions have been asked before by other posters.
As far as the spiritual side of aikido is concerned. In my opinion, you can take as much or as little of that side on board as you like. Aikido is a very personal thing and sure, some people find spiritual comfort in the art, others don't.
Two members at my club are christians and are still able to practice the art without it clashing with their beliefs.
I hope you find aikido to your liking.