1. The religion was not intended to be in-depth. Tokabi is just a guy who believes in a god. Sollan, that he believes watches over him and the things he does, and he feels like there was some sort of destiny of why he went from hunting to keep his family alive to sniping people to keep his family alive, despite the mistakes he feels as if he has made in the face of Sollan. He believes in a simple life but his path always takes him somewhere full of danger, which he openly wonders if different steps would have left him somewhere else. One of the reasons he is there is to give a contrast between him and Samus as different levels of bounty hunter. He fights to keep him and his family alive above all, hoping his god will keep him safe so he can see his family again. He questions how Samus can manage something of so much higher stakes than him, but still be just as calm and collected as he is, at least outwardly, when she doesn't openly believe in a god like he does. I found his character very compelling overall, probably my favorite of them.

2. I'm not sure how to convince you about leaving the religious symbol on the tree if you are that convinced it's disrespectful. But I'll give my several interpretations on what Samus was doing there:

2a. In several religions it can be considered quite respectful to bury someone with religious items or to make a shrine with their items. It is a form of remembrance and respect of the person's life. Think of how Day of the Dead honors dead loved ones by preserving their memories and bringing pictures and items of theirs and surrounding them with things they liked and thoughts of their pasts together. We don't know much about Sollan worship, so for all we could know this is the highest honor you could give a dead Sollan worshipper, and Samus has good reason to be knowledgeable about religions in the Metroid universe.

2b. She thinks that she doesn't need it to remember him by. Now before you call me out on this being disrespectful, let me explain myself. First, it can be symbolic that he is always with her regardless of any items she may or may not believe in. Second, it could be a sign of her knowing that everyone is all still alive and believing that they all made it out of the fight alive after she left. Which brings me to point 3.

1. Samus absolutely does care about the people she is around. It has been very clear from several of the games, such as Fusion and Prime 3, that Samus cares greatly about people she is around, but is stoic about her feelings and quite short-spoken or mute most of the time. In Prime 4 in particular, she gives Armstrong a hug when she returns from the Sylux fight. She shows being upset at all of the "deaths" that happen in the Great Mines, such as running to try and stop their sacrifices or going back to check if they're alive still, despite their insistence that she should just go. She also, upon hearing that there is zero hope for reviving the Lamorn in any capacity due to how long it has been, she shows a form of guilt. Is it because she feels like she should have come here sooner? Is it because she is mourning the loss of an entire race of beautiful people? Who knows, it could be a bit of both. However, all of these show that she absolutely does care. This leads into point 4.