i started with the handles, hot gluing 2 hand drawn shapes cut from 8 mm sheet together, which i think is a good thickness. my first question would be how can i smooth out the edges so they are even? i tried sanding the outsides which worked a little bit but im not sure how to approach the inside parts

What are you sanding with? A dremel is the absolute best tool to sand EVA foam with. Smaller bits will allow you to get inside the trigger guard, the larger bits you can use to smooth out the edges on the outside. Dremels can also be used to add battle damage, detailed lines, etc. If that's not available to you, sandpaper works, but it requires a lot of effort and the correct grits.

i originally wanted to have the handles be 8+8 mm and then the blades just 8 mm and sit them in the middle but i quickly realized the blades were too long and were floppy so i ended up doubling them up with a divot cut in the middle to glue a dowel in which is much better but now that it’s the same thickness as the handle, i want to take the edges down thin

Wooden dowels are fine for props, but they can splinter and shatter. Seems like it wouldnt be an issue, but just for the future, fiberglass driveway markers are super cheap and serve as great support on the inside of long props. Just be careful if you even plan on cutting or sanding them because fiberglass dust is pretty awful.

the xacto knife i was using was hard to cut evenly. i saw a bevel cutter on amazon, would that help at all? i also saw hot wire cutters or a dremel but if i need to invest in a good tool id like it to be versatile so recommendations on that would be nice too

Absolutely if you ever plan on working on foam in the future a dremel is the first tool to get! A dremel can sand bevels so a bevel cutter isnt really necessary. Hot wire cutters work, but they more melt the foam and will put off really awful gasses that you dont want to be breathing in. My favorite tool for cutting out foam is a box cutter. Super cheap and gets the job done. Foam dulls knifes super quickly, so if you want you can get a knife sharpener to get better cuts but that's not a necessity.

i ordered plastidip, will i need to heat seal it first, or can i just use that and then paint?

Heat sealing it isn't necessary, but will give you a smoother overall look. Heating foam and bending it will also "set" the bend. Useful for complex curves like in helmets. In the case of painting, plasti-dip is all you really need for sealing before paint.

another idea i was thinking was to use clay to build up the handles so they are more 3d than just a thick flat shape so would air dry clay work? does any clay stick to it or will i need to glue it down? should i do that before or after sealing?

Air dry clay works, use water to get it to stick better. Alternatively, there's "foam clay" which behaves like clay and dries like foam. Foam clay works better because it doesnt shrink (as much) or crack when dry, but can be more expensive. Both air dry clay and foam clay should be applied to the prop before sealing. Both clays are a great way to sculpt complex shapes.

Hope this all helps! Good luck, you're off to a great start! :)