If you're fighting against equal to advanced war tech enemies, keep your armies on the defensive and plan on fighting them to a white peace. This is because if you try and go on the attack against an enemy army with stronger war implements and a near enough body count to your army, they will get slaughtered. Your manpower will rapidly be depleted and your armies will not be able to reinforce fast enough, and more likely than not the enemy army will go on the attack and continually route your army and take more land. Practice fighting wars on the steppe states between you and Persia.

Secondly, since you're also taking control of a country with the aristocracy and landlords in control of the government, it becomes your best interest to set your taxes to 'very high taxes' and utilize the surplus tax funds to build more construction sectors and increase the rate you're industrializing your state.

Set 'promote social mobility decrees in your most populated provinces so you can increase literacy and your research rate while not having an education policy.

Lastly, try to beeline towards getting the railways tech so you can further industrialize without stumbing over infrastructure limits.