Building plugin through the Gradle Workflow

Dear all,

I am developing background plugin for IDEA 2019.2.

Following the documentation Building plugins with Gradle.

Also as a reference using the examples of plugins.

When I am ruining runIde task through the Gradle tasks my background plugin works.

When building plugin jar (ruining buildPlugin) to installed through the Settings -> Plugin section plugin not works.

Developing plugin through the DevKit working fine for the same plugin and also for DevKit we have Deploy Plugin documentation.

My plugin configurations:

plugin.xml

<idea-plugin>
    <id>com.metaring.platform-plugin-idea</id>
    <name>MetaRing Plugin for IntelliJ Idea IDE</name>
    <description>MetaRing Code Generation Plugin. For more information please visit to our web site</description>
    <vendor email="info@metaring.com" url="http://www.metaring.com">MetaRing s.r.l.</vendor>

    <!-- Product and plugin compatibility requirements -->
    <depends>com.intellij.modules.lang</depends>
    <extensions defaultExtensionNs="com.intellij">
        <postStartupActivity implementation="com.metaring.plugin.idea.activity.MetaRingPostStartupActivity"/>
    </extensions>
</idea-plugin>

MetaRingPostStartupActivity.java

.......
.......
.......

public class MetaRingPostStartupActivity implements StartupActivity {

    @Override
    public void runActivity(@NotNull Project project) {
        System.out.println("Hello World");
    }
}

build.gradle

plugins {
    id 'java'
    id 'org.jetbrains.intellij' version '0.4.9'
}

group 'com.metaring'
version '1.0-SNAPSHOT'

sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.12'
    compile group: 'com.metaring', name: 'platform-ide-plugin', version: '1.0.7'
}

// See https://github.com/JetBrains/gradle-intellij-plugin/
intellij {
    version '2019.2'
}

Questions: 

0. Should I have some miss configuration ?

1. Should I am restricted to install plugin as a jar manually, if I am developing plugin through the Gradle workflow ?

2. Do you have any Deploy Plugin instructions for Gradle Workflow case ?

3. Should I have to have zip instead of jar plugin, if have external libraries as mentioned in documentation ?

NOTE: I have another question here which is about troubles during buildPlugin task.

Thanks in advance for your reply