Biggest tip is of course "read the full manual," applies pretty much to any game from the 90s and earlier.
I remember playing the demo back then, accidentally finding out that I can right click to actually aim the bloody gun and hit something made the entire game click and come together as the bestest thing ever.
Some of the less obvious features: you can hold Ctrl and click to open an interaction menu - this lets you, for example, close containers.
It also lets you steal stuff from opponents, but you need to do it quick and pummel them until they're unconscious (not dead). It's a bit risky, but that's pretty one of the few things unarmed combat is good for in this game.
(and I'm not sure if it's even in the manual).
Is there any indicator how often mercs should sleep? How to i sell excess loot? If i bandage my mercs why is their HP bar in brighter colour than before? How to bandage after autocombat?
Sleeping goes like this - mercs have a stamina bar which depletes with exertion and refills right back when you let them catch their breath for a while. As you perform more strenuous tasks (travelling, assigned jobs, etc.)
the fatigue bar will start depleting permanently, limiting your max fatigue until you sleep it off.
Mercs will typically tell you when they require shut-eye, but you may decide to put them to bed earlier if you need them at peak efficiency (e.g. for combat).
Bandaging with first aid kits only stops blood loss, you don't get any hit points back this way. The merc recovers by resting. Assigning mercs with high medical ability as Doctors (you'll need a doctor's bag for it) helps to speed this up.
I typically don't autobandage after combat (unless there's an emergency), it's a good opportunity to gain a few points in medical ability
When it comes to selling loot don't worry about it too much in a vanilla game. Your main source of income will be liberating towns and talking to mine foremen to setup the funding scheme for your operation.
The rest of the income is peanuts. I'm not 100% certain if selling loot from inventory through altr-click is a 1.13 mod feature, but the correct way to sell stuff is by finding vendors. The nearest guy to buy and sell guns
is in San Mona, but you will need to do a minor quest to gain access.
Random Tips:
Always check the whole map and talk to every NPC (have good leadership on your talker). It's possible to discover things like quests and loot.
Same applies to the map, you can find hidden caches and sidequests if you stray off the roads. Though you shouldn't be wandering off alone.
If you come across a locked container, try kicking it open. The merc might protest that it won't budge, but don't be fooled.
Alternate between kicking and prying it open with a crowbar until it eventually pops open. Might take some time depending on strength.
When it comes to mercs, most of the time you'll get what you paid for. However, don't get too obsessed with marksmanship,
while it's good to have a few guys who can hit the broad side of the barn, it's really easy to train by just shooting things,
and pretty much any skill can be trained with practice and high intelligence, and lower skill values actually train quicker.
It's the physical stats that are the most demanding to train (strength, dexterity and agility),
Same goes for merc expert training (night ops, sneaking, auto weapons, ambidextrous etc.) so be on a lookout for good deals and "diamonds in the rough."
For example, Len is a good, dependable early merc that covers a lot of bases for you, but won't develop his stats (if he does, it's a known bug in the game).
Dr.Q might look like a poor choice because of the 60MRK, but he's got fantastic physical stats and once you raise the MRK above 70, he'll actually start hitting things.
The "learning by doing" system is abusable, but I recommend not wasting time grinding perfect stats. Just play the game and let it flow naturally.
Even mercs that look useless can be valuable for the comedy value. Half of the game is listening to banter and discovering interactions between chars.
For example, the M.E.R.C guys seem useless, but you can use them as mules, and it'll eventually unlock better guys.
Ask away if you have any specific questions.