First time doing-it-myself, please give me some advices on these components

Sounds like you are trying to find instructions to boil an egg with a cookbook from the culinary arts, it won't be there.

The bulbs are just twist off replacements, find the corner bulb (will not be on when you have your headlights on) and replace. Don't over think it

SM-N900P ?

 

The alignment, any shop capable of alignments can do this for you.

The water pump and belt can be replaced in about 1 hour (depending on your skill level). Here's a good video

 

The engine water pump is located on the passenger side of the engine, near the bottom. It has a large, black pulley. The pulley is driven by the serpentine (drive) belt.

This water pump tends to develop leaks on the 2nd-gen Prius. This is why they need to be replaced. You'll want to replace the entire pump. Coolant leaks show up as pink, crusty buildup or pink streaks around the pump, inside the pulley, and sometimes on the underside of the hood. It's pretty easy to replace (and the serpentine belt is easy to replace at the same time). The most difficult part is probably getting the air bubbles out of the cooling system afterwards.

This is where I got my water pump--it's a good source for discounted, mail-order genuine Toyota parts. They also carry the serpentine belt. I learned about it here on the forum.

2004 Toyota Prius Parts - AutoNation Toyota Gulf Freeway Parts

Also pick up a gallon of Toyota SLLC (Super Long Life Coolant).

You'll want to remove some coolant from the radiator first. The drain valve is difficult to find--I believe it's on the lower, drivers' side of the radiator if I remember correctly. The radiator also has an air bleed valve at the top that opens with an allen wrench. The coolant drains much better with the air bleed valve open, and it really needs to be open in order to refill the radiator with coolant.

Don't forget to loosen the nut in the center of the belt tensioner pulley to take the belt off--otherwise the tensioner won't loosen.

There are various strategies to get the air out afterwards. It helps to park the car on an incline with the nose uphill. Fill the radiator as full as possible with the air bleed valve open. Then close the air-bleed valve, turn on the car and turn on the heater--this will help keep the gasoline engine running and help get any air bubbles out of the heater coolant loop. Pressing the go pedal also helps keep the engine running. You can also use maintenance mode, described in the video. Air should work its way to the radiator fill neck, and you'll be able to add more coolant. It took me a few driving trips to work the rest of the air out (you can hear the air gurgling in the system as you drive). Drive a few, gentle, short trips to prevent over-heating until all the air is out and the coolant level stays at the top of the filler neck. I left the radiator access cover off for a while and kept adding more coolant after each drive until all the air was out.

Here's a how-to video:

 

You don't have to worry about high voltage for most work, including the engine coolant pump. The high-voltage system is disabled when the car is powered off. High voltage conduits and connections are colored orange. You only need to worry about high voltage when servicing components of the high-voltage system (inverter, HV pack, etc).

Most multimeters don't have current (Amp) measurement built-in. Voltage measurement is more common. To measure voltage, place the meter in the correct mode (AC volts/DC volts and numeric range, if equipped) and connect the meter in parallel with the circuit.

If your meter happens to be equipped with current measuring ability, it usually needs to be placed in series with the circuit (disconnect the circuit and then complete the loop with the meter), unless the meter has a coupling device (large ring sensor) that can be placed over a wire.

 

The high-voltage stuff is pretty well concealed under the hood--you have to look pretty hard to find any orange, and it's not energized when the car is off. No need for electrical gloves while working on the engine.

Of course a lawyer would throw in a bunch of small-print cautions here, but for all intents and purposes, you don't have to worry about the high-voltage system when not actually working on the high-voltage system.