[@Lucius Cypher] Let me break that down to individual things and evaluate their intensiveness for educational purposes.

[list]
[*] Moving the twenty feet onto range, assuming you are 30 ft. away of the kobolds (which you are) costs the 20ft. out of your 30 ft. pool.
[*] Throwing a harpoon is an action of the attack type. You know the drill.
[*] Drawing the harpoon for an attack is a special case, something what you are granted one per turn unless you take a feat that allows more of it. The feat I speak of is "Dual Wielder", PHB p.165.
[*] Drawing the machete falls under the ruling above, rendering doing both impossible.
[*] Equipping your shield costs 1 action, as does putting it away (PHB p. 146).
[/list]

[h3]Now, a quick refresher on a turn in combat of 5th edition: What you can and cannot do![/h3]

Each round, you have your movement, action, bonus action and your reaction. You generally use most of those on your own turn with the reaction being, well, your reaction to someone else. If you can do something as a bonus action (other than attacking with an off-hand weapon) it is likely a spell or a class feature, so you'll know if you can do it. Your movement is, well, your movement. Limited only by the maximum amount per turn, you can for example step 10 feet, attack, step 10 feet, shout, and move the remaining 10.

Now, actions are probably the most varied of the bunch. You can do many things, all neatly described in PHB p. 192 and onwards, alternatively available in the Basic Rules linked on the Characters tab. No "move actions" in 5th edition, nor "5-foot step".