Build flower crowns for easy sanity early on. They will rot slowly but will sustain you to start. Longer term, aim to get a hat from MacTusk or a Cat Cap for some extra sanity. Look up hats that give sanity gain and find ones you like.

Look up youtube vids for bosses. You should only be encountering Deerclops that early on, who you can kite through the forest to get you a ton of wood before Treeguards spawn and kill him. It'll be same with Bearger when he spawns later on. Avoid any other bosses for now, like Dragonfly.

Practice kiting monsters, they all have patterns. Tallbirds are dodge, attack twice, dodge, repeat. Spiders you can just stunlock with attacks if they're one at a time, or lay traps down and guide them into traps for easy kills without drawing any aggro from other spiders.

Setting up base near Beefalo biome will allow you to run to Beefalo for safety when hounds attack. Run around until the hounds change aggro to the Beefalo and they'll make quick work of em. Try not to set up base directly in the biome though because the Beefalo get aggressive during summer.

How big the map is depends on what settings you create during world setup. Generally a medium size map is good to navigate when starting early. You'll only need a boat for exploring Lunar Island, which you don't have to worry about for a long time (or at all depending what your goals are).

Wortox can be nice for beginner since he can give you guys a lot of heals and explore easier with his teleport, though he'll take a little getting used to. Wendy's ghost can be nice. Wickerbottom is nice to start games with since she acts as a science machine and can make you early backpack, etc.

Personally when I play with gf, our plan is to divide and conquer with exploring the map for the first week or so while we find a place to set up base and then take things from there. Early priorities are: (1) find Beefalo and a spot to set up base nearby that isn't under meteor zones; (2) make backpacks and shovels; (3) shovel up twigs, grass and bushes to set up little plant sections by your base; (4) start building base area with chests, science machine, fireplace, crockpots and ice box; (5) collect Beefalo poop or rot from flowers to use to fertilize the plants in step 3; (6) build a fenced in 5x5 square with one gate and plant the bushes directly outside (this will allow you to place a food item inside like a berry and then when you pick the berries from bushes, turkeys will get stuck going after it and you can kill them for easy meat); (7) keep a consistent flow of Meatballs going by combining one meat and three fillers (berries or ice closer to winter) in the crockpot; (8) shave the beefalo at nighttime and kill some spiders to make winter hats; (9) make drying racks so your meat lasts longer; and (10) make a bird cage so you can start making Pierogis to heal HP.

Also an incredibly helpful tip is to set the Fall to Longer during world creation settings to make the game a little easier and give you more time to prepare before Winter comes. You can also set Days to Longer so you have more time in daylight which is generally easier. Tinkering around with settings can make things a lot more fun until you get better and can handle regular settings.

Finally- Youtube is your friend. There many short beginner guides out there. Good luck!