Essay time, sorry lol but I hope this helps!
DnDBeyond, a very helpful website, has an encounter builder that is very helpful for balancing encounters. it uses CR (combat Rating) to balance between the party and the enemies. A good thing to remember is one hard enemy will be easier than multiple medium enemies, as action economy can take out even a skilled party if they're overwhelmed. There's a lot of ratios and dice rolling stuff i could explain if you want, but pretty much just know that a party is more likely to be killed by a swarm than a single enemy. If you want to play nicer to your players, or if they're struggling, make sure to play the enemies different. For example, the evil goblins are going to each target one person instead of ganging up on the one guy in front (the party will likely divide and conquer, so enemies can too!), or maybe they see the biggest guy in the most armor as a threat and are going to priortize them over the squishy wizard. This is a way to make it more fair or less fair even after the fight starts, but I suggest not changing the stats once the fight starts (before hand is fine, like removing an enemy or swapping them for a more or less stronger one), but your players will likely notice if the enemies suddenly have less hp or are 'missing' all their hits. Don't lie about dice rolls is the main one, even if it helps the party it will do more harm than good in the long run.
Just keep an eye on your character's spellslots and ability slots of they have them, as after a fight or two a level one spellcaster will be out of abilities and useless in a fight. 3 easy encounters in a row can be deadly if everyone's low on health, spells, and supplies. Just try to pace it out so they don;t get burnt out too fast too early on the adventure. There are resting mechanics in 5e, but they can only do so much before a full night's rest is required. (also if you're looking into survival mechanics, definately look into 5e's short/long rest and exhaustion system!)
Another thing I want to mention for encounters is just a homebrew rule my DM uses. When someone is down, or unconcious, etc, they usually with D&D 5e get 3 death saves, above 10 is a pass and below 10 is a fail and so on. They way he rules it is that he the DM is the one to roll them, it adds suspense to encounter and forces players to think on their feet and worry more about healing without metagaming since no one knows. Besides that, decide how you want resurection to work. We use a dice system our DM came up with where after a certain number of dice/death rolls, the characters get too tired to return. Others use a 3 lives rule, or they keep upping the cost to res someone. ofcourse those are preferences, you can have res just be a visit to a temple or unlimmitted via spells and such.