Artificer's Medium Armor Mastery and gear training

You have practiced moving in medium armor and trained in weaponry to gain the following benefits:

• Wearing medium armor doesn't impose disadvantage on your Dexterity (Stealth) checks.
• When you wear medium armor, you can add 3, rather than 2, to your AC if you have a Dexterity of 16 or higher.
• You Gain proficiency in Martial weapons 
• Choose expertise in both a skill and tool
• choose a ability score