1st off it might help if you don't look at them as units they are nothing like the units you now have, but more like a cross between your general items in the way that they add a % bonus to your units and also in their rarity (they are color coded the same as your general's equipment but with a extra class on top orange) and your Phylarch in the way you fight the warlords to get points and also the way energy recharges (needed to fight the warlords).

   What to keep and what not to keep. 

You will see when you do the tutorial that you are going to need to trade a lot of these units in to upgrade other units. Anything below rarity III (blue) you are likely to want to trade in within a few weeks at most, so don't waste any of your new emeralds on them other than what you need to use to finish the tutorial. As a rule anything with a of rarity III (blue) or higher you want to keep at least for awhile.

   Upgrading units. 

I would not ever sacrifice units to upgrade unit levels, only sacrifice when you need to complete a mission, don't use units to improve unit rank unless you are planning on spending you cash on these. You will struggle to get the BASIC bonds you need without burning units, it's cheaper to buy energy recharges and i would only do that if there is a champ event on and you have a 50% points boost running. save everything like the points boosts and any recharges for the new events, you will want to max the event (it's not too hard and i will explain how to go about it later).  

   What units to upgrade 1st 

depends a lot on your own game and stile, but to me the cap def unit should come 1st at least as soon as you have one rarity II (green) or above and changed as soon as you have one of better rarity. try to get this to unit up to rank 4 level 15 asap (no higher do the last 15 levels in one of the new events when they start). Then send it to the cap (you do this the same way as you send any other unit to the cap, you should see the new unit at the top of your unit selection window when you got to send reinforcements to it. It will be auto selected). 

Also the city def unit should be done early. They only cover units that are with them so you are going to want more than a few of these for walls in the end, so i would keep any of rarity 2 and above no matter if you have more than one or better ones also this is where you will want to spend your grade II skill stones i would think as these are the units that you are going to want to keep the longest (careful with these they auto select when you go to send reinforcements to cities some thing you may not want to do).

 Outside of an event. 

Fight as many of the new warlords as you can as often as you can. Finish each of the new warlords in one hit, do only the highest level that your unit can clear so dont hit a pp higher than your units Attack power Vs warlords but the same is fine. Try to get as many units to rank 4 as you can. when doing this do it by getting 1 to rank 3 level 25 and 3 to rank 3 level 1, don't waste energy and time upgrading the level of those 3 units you are going to sacrifice in upgrade the rank 3 level 25 to rank 4 and the same when upgrading the lower ranks too.

  In an event. 

Turn domination on if its not on already to cut travel time from 2 mins to 30 secs. This is the time to use those 50% boosts and buy energy recharges and get those rank 4s to level 30. upgrade all the rank 4s you can to level 30 with the points boost on this is were most of your event points will come from plus each of the rank 4s you get to 30 will give you an extra 100 of the new emeralds. T

this pays for the energy boosts you are using as well, so even the grade 4s that you don't want to keep to level 30, its the best way I've found to grow without spending cash you should even make a profit in emeralds from it if you do 3 warlords at the same time while you have the boosts on. 

Note that the 3 warlords NEED to be of a dif level dont send them to the same place! it takes some doing as they only take 15 secs travel each way but once you have got the hang its not too hard and doing them this way will save you real cash and a lot of time in the long run. It will get boring trust me but it's worth it if you have the time even without spending doing this for a few hours will place you in the event. 

To finish top 20 is around 6 hours work but max reward will be reached in a little over an hour. However in the very 1st event you might run out of emeralds 

  If you want to spend. 

Quite a few packs with dif things available but i would only ever be tempted to buy the packs that contain the 2 holy summoning bonds, everything else you want you should be able to get in time if you follow what i've said above. 

I would not be tempted to buy the epic summoning bonds with your new emeralds they tend to throw out grade IIs far too much for my liking. 

They are far too over priced for a small chance at winning a grade IV unit in my opinion (Sorry Plarium!). 

Once you have built up 2000 or so emeralds then they maybe worth a look but i wouldn't till then. You are going to have to buy basic bonds and a lot of energy recharges in the events.

   pros and cons I can see coming up in the 1st few weeks for the coa. 

Against the more active players that have coined their new units city walling will be quite a bit less effective and a little less so against everyone else. the same with pans and caps. within 3 to 4 weeks of these units coming out some will have a unit % boost of 70% or more against these targets. Over time i foresee these effects dropping off as people that haven't hammered their cc accounts catch up. It's just something to be mindful of.  

Grade 5 Guardians 

These are incredibly rare and even when purchasing holy bonds you are not guaranteed they will drop, please, exercise caution to avoid unnecessary spending, it is a bit of a lottery and the feature hasn't been around long enough for the drop rate to be even roughly calculated. If you are happy to spend the money on Holy bonds obviously that is your right however they are ultra rare! 

Bonds dropping in game 

If you have 100 basic summoning bonds already no more will drop until you use some up!

written by of one of my coalition members