The balancer is responsible for selecting players. The balancer "checks" your highest tier ship and amount of battles on this ship. It's set as priority for balancing. So if 2-tier and 5-tier ship meet in the battle it means that:
a) 2-tier ship has many battles and isn't considered as newbie
b) 5-tier ship has few battles and isn't upgraded
c) for some reason players take lower ship having higher ships in the port
Moreover, some ship levels are united into one ship group.
This system was introduced so that players intentionally did not leave the battle (for example, to preserve good statistics if the battle was lost in advance), substituting members of their team. Unfortunately, the system will not be changed at this stage of development.
1) You will not spend silver/gold if you do not use the modernizations in battle.
2) You spend an amount of gold/silver equal to the number of activations of the modernizations when using this modernizations in battle on a particular ship.
3) After that, you can use the modernizations in the amount in which you purchased it during one battle on this ship.
Sometimes updating tasks takes some time. However, it will be credited to your account in any case. Try to re-enter the game and check if the status of your task has been updated. Also check if you have met all the conditions for completing the task (e.g. for one battle or for one shot, etc.).