which class to play

Try to play around with all classes, sadly ultimately what determines a class is their ultimate, a skill which will take

quite a lot of time to get unless you spam AI games for mastery points. 
If you want to play a tanky class go for Longsword, Shortsword, Poleaxe, Maul
If you want to kill units from far play Longbow
If you want to kill heroes easily play Musket, Shortbow, Dual Blade
If you want more all around classes play Spear, Glaive, Nodachi

which gear to get

Pre Level 30 you won't have to care about what armor you use, just use whatever  you find.
After that you will want to use the blue schematic weapons and armour, Rogue, Carnifex, Guardsman sets.

Using purple schematic armour is extremely rare and only a handful people on each server do.

which attribute points to use

Since you're still in the stage of figuring out which heroes you like i would advice a build that you can use

regardless of which class you play, for that you want to put points into every attribute equally.
So at level 60 you would be 35 STR 35 AGI 35 ARM 35 TGH

Once you know which class you want to main i would advice checking the recommended attributes for that class

under the Heroes tab of this website.

You only get 5 free attribute point reset books from the game so spend them visely.

If you want more you need to pay real money to get them.

which units to get

To answer this we're going to focus on units that you can use now to great success that will remain

powerful even in lategame.

Serfs
You may want 5x Level 7 serfs, these are the only units giving you a bonus when gathering in the 

open world, this can save you tons of bronze and gain you silver when they make your life easier gathering for unit kits or exotics to sell on the market for silver, but this is by no means a requirement.
Woodcutters

These may seem as weak units but they fill a great spot as budget units for only 40 leadership, they get a charge once

leveled up properly which makes them decent adversaries in battle.
They also have no unit kits which means you will never need to spend bronze to repair them.

Pike Militia
Pike militia is a really strong unit once maxed and a staple in many maxed level players loadout.
These should be your first choice to get maxed.

Seasonal unit
A cheap seasonal unit can be very strong without you needing to spend a lot of time or resources to get them.

Most notable right now for you as a beginner are Namkhan Archers S2 and Condottieri guards S3 

Spear Sergeants

These should be your first choice when getting a higher tier unit.

Spear Sergeants will open up Expeditions and Rebel camps for you to easily complete them without any unit losses.
They are strong units and fairly cheap to get with Honour so try to get them ASAP.
Lategame Units
After a certain point you want to start working towards your lategame units, these are 

S2

Namkhan Archer, Kheshigs

S3

Pavise Crossbowmen, Fortebraccio Pikemen, Falconetti Gunners

S4

Azaps

S6

Arminger Lancers, Liao's Rangers

S7

Berserkers

S8

Immortal Garrison, Dynastic Guards(Modao)

S9

Axe Raiders

Cavalry

Winged Hussars, Monastic Knights, Cataphract Lancers, Fire Lancers, Rattan Rangers

Ranged

Tercio Arquebusiers, Imperial Arquebusiers, Imperial Javelins, Javelin Sergeants, Imperial Archers, Vassal Archers

Melee Infantry 

Imperial Spearmen, Imperial Pikemen, Iron Reapers, Palace Guards

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