>>11502177I wouldn't really trust Reddit at all when it comes to Tamagotchi's vpet elements, most of the posts there seem to focus on shallow aesthetic aspects more than anything.
That said, releasing seems to go in order of oldest out, so if you have a fifth Land Tamagotchi you're about to release, for example, your very first one will be the one to go. Theoretically, you can store up to 13 characters total, 4 for each biome + the one you're currently raising.
Unlocking biomes is in a set order. For Pink Land, I unlocked Water at Planet Level 4 (raise a character to adulthood and then get a new baby), and Sky at Level 6 (raising that new character to adulthood). Checking out Japanese YouTubers, the order seems to be 
>Pink Land: Land default -> Water Lv4 -> Sky Lv6>Blue Water: Water -> Sky -> Land>Purple Sky: Sky -> Land -> WaterAs I mentioned before in my further complaints section, you can't swap biomes during the teen and adult stages, so actually seeing what the guys you raised in other biomes is up to is kind of a hassle, so I personally ended up just sticking to Land after trying to raise one in the Water biome.
On the topic of biome swapping, apparently the method to get Dekababymarutchi is different from what was advertised. The guidebook says to leave Babymarutchi idle for four hours, but in actuality, you end up getting him by constantly swapping biomes during the baby stage to prevent him from properly getting accustomed to one biome and growing that way. A lot of JP players on Twitter accidentally ended up getting him naturally through biome swapping rather than neglect.
Also, for people struggling to get the right food items early on, since child->teen growth is dependent on what's fed but the availability of items is so limited before the shop starts selling food, you can cheese the system and get more Egg Hunt chances by changing the clock to 11:59pm, waiting a minute, and changing back to the proper date. This resets the daily limit for it.