This is my first tutorial, so please bear with me. I am sure I will be missing things as I frantically search my mind to make sure I am not missing things so if you need any help or input I would be glad to help.
This is how I made my plague doctor costume.

Step 1: Mask

I found a template to create mask on instructables by Vivid-and-trivial. You can find it here https://www.instructables.com/id/Plauge-Doctor-Mask/

Once the fit is right cut each piece out of craft foam. For easier use, you can use craft foam with adhesive on one side.
Place the adhesive side onto the wrong side of your fabric. Cut the fabric with enough extra around the edge to be able to wrap around the foam to hide it. (Do not cover the edges yet.)
Line each piece of foam with wire. I used 18 gauge wire I got from Home Depot, but any craft store should have it in the jewelry making area.
Cut into the extra fabric bordering the pieces in about 1 inch sections; this will make wrapping the curves easier. Once each piece of foam is laid onto the fabric and outlined in wire wrap the extra fabric around and glue into place. Follow the instructions used to create the template to assemble the pieces together.
For "rivets" paint googly eyes with a color of paint that goes well with the fabric used. I used mini googly eyes painted with a metallic acrylic paint. Attach the googly eyes wherever straps attach onto your mask. I used two side by side at each point but on other masks I noticed they were used in threes creating a triangle shape.

Step 2: Hat

For the hat I used wire hangers, plastic folders, and fabric.
DISCLAIMER: I couldn't find any hat making tutorials online that I liked so I did this as a trial and error experiment. The end result looks ok, but I did not add extra room for materials so it is tight and sits ontop of my head instead of on it. Also, the wire is unforgiving and creates a heavy hat. If you can find a better way to make the hat I would suggest doing so. I did not because plague doctor hats are extremely unique and I couldn't find any hats I was comfortable with using.

Make a template out of paper to ensure the hat will fit.
Trace a ball cap onto paper to get a general shape and size. Cut out the traced shape and try on. If it does not fit, add or cut out paper until you are happy.
Open a folder and cut off any borders or pockets. Trace your hat template in the middle of the folder. (Very little of the fold will be used and won't make a difference in the end.) Cut an extra 1/4" from the circle opening to add room for materials.
Draw a shape 2" from the open hole to create the brim. I assumed it would be a circle, but mine came out as more of an oval.
Outline the biggest (outter edge) and smaller circle (inner edge) with hanger wire. Secure into place using hot glue. At each curve and in the middle of each straighter area place a line of wire from the small circle to the large circle. I ended up with 8 lines in between the circles. This will let you bend it to your liking. Wrap the piece in fabric with 2" left over. This allows the brim to be attached to the body of the hat.
Cut a strip of a new folder long enough to line the inner circle. This will be the body of the hat. (If the strip isn't long enough, cut out more from left over folder and tape them together.) Plave inside the brim and secure where ends overlap. (Superglue will NOT work on the plastic folder. Tape or hot glue is better to use.)
Trace the opening of the hat onto a new folder to create the closing at the top of the hat. Cut out the top and secure using tape. To create the shape of the wide to thin on the body I used clear tubing from Home Depot at 0.5" thick hot gluing it into place around the top. Cover in fabric. The fabric will need to fold in areas to follow the curve; glue each fold down to create a crease.
Place the top of the hat into the brim between the extra material left over. Glue the material to the top of the hat keeping the outer material short. This way you can cover it with the band but it will be secure together.
Cut a strip of fabric about an inch thick to use as the band where the body and brim meet.

Step 3: Needle and Holder

I used a syringe for the body, but as long as it has a similar shaoe you should be fine. Because the antique syringes are quite large I wrapped mine with 2 layers of craft foam.
Cut a long piece of heavy gauge wire for the needle part. Wire hangers work great! If you are not using a syringe, you will need to puncture the area where the needle comes out. Using a glue gun, create a ball of glue at the end that will stay inside the syringe. The ball needs to be big enough to keep the wire in the tube.
I used a thin water bottle lid for the top. Using a medium gauge wire form a circle with a long stem on it. Simi6to a bubble wand. This will be the "plunger" part for the thumb. Puncture the middle of the lid and insert the piece making a ball of glue on the inner side to keep it from falling out. With more wire, make 2 shapes similar to a 9. This will be the area your fingers go through. Puncture the water cap on each side of the thumb piece and place the pieces in. The stem needs to be next to the thumb piece with the circles pointing out. These can be glued into place. Super glue works best to keep the area cleaner looking and free of bumps. If you want the plunger to move do not glue it.
Glue the cap onto the syringe.
For a cleaner look you can wrap the body in masking tape.
Paint a desired color.

For the holder cut a rectangle from fabric long enough to house your needle leaving an extra 1/4". With right sides together, sew along the edge leaving an area open. Turn the fabric inside out and close the open area with top stitching.
Cut a small strip of material at desired width long enough to go around your needle without overlap. Glue onto the rectangle of fabric you sewed in desired location. I used small glass bottles so my rectangle was quite large. If using vials repeat the process of creating strips to hold them. Add 2 strips of fabric in a loop fashion in the back of the rectangle where it will hang from your belt. Keep in mind the loops need to be big enough to fit onti the belt.

Step 4: Pouch

On the back of your fabric draw a large circle. I drew a circle about 8" in diameter and my pouch was a lot smaller than I expected.
Punch holes to thread string used to pull closed into the edges of the circle. I plaved mine 0.5" from the edge and 1" from each other. Weave string strong enough to pull the material closed through the holes leaving 2 long strands next to each other on the right side of the material.
Cut a strip if material to use as the closure/loop. This is what I used to slide it onto my belt. Directly straight back from the strands in the front, glue your loop on the right side of the material. Cut 2 slits in the front of the loop and thread strings through tying knots at the end. Pull strings to tighten into a pouch.

Step 5: Embellishments

I found a coat at a local thrift store. I removed all of the buttons and belt loops to create more of a robe look. An infinity scarf can be used to cover the neck and create a hood under the hat. I used an old stained tea strainer and put a long chain on it. Attached to the front of my belt it created a smoke ball. Leather boots, a walking stick, a lantern, and all of the handmade items tie the costume together.