If you are a low spender, a good deal is buying the 0,99$ castle skin pack every day.
The goal is save as many tickets as possible spending as less as possible in order to buy castle skins.
Best buy is the Cloud castle skin because it gives +10lv Hero.
In geneal the shop is very good so if you alredy have the cloud castle you can buy others castle skins
or even other items like queue skins or rare pet chests that are usually great deals.

In order to avoid misclick and claim healing soldier before an event
we recommend to delete the notification.
Click on your profile picture -> Settings -> Other

Each pet will give you buff even if it's not deployed.
Only the stronger copy of a single pet will count to give you buff.
So it's good to have once copy of all the pets.
In order to do that one of the best way to buy the pet at the lowest price is
buying the Rare Pet Choice Box from the Castle Skin Pack event for 60 vouchers

The buff the really matter and makes the difference are:

Harvest: speed construction

War: buff and march size

It means that untill Castle lv. 40, and most of the bulding less than lv. 40, Harvest makes sense.
After level 40 the time required to build is much less, so you can switch to War Lord.
If you are planning to do many upgrades for an event you can switch back,
but don't the 7 days cooldown to switch again for free