I have some 28AWG Kanthal wire and lets say i just wanted to make a heating element. I will connect the wire to a 5.0 V dc power adapter. Is there anything i have to put in series with the wire just to make sure everything works okay, or can i just have it connected to the power supply with nothing in series.

Depends, how much wire are you using and what's it's total resistance? Also what is the max amperage your power source can handle. Keep in mind that voltage divided by resistance tells you how many amps it will draw.So the lower the resistance on the wire the more amperage it will pull. If your power source can only handle a max of 1A you'll need a coil of wire or combination of wire and resistor that equals about 5 Ohms. Preferably a little less so your not over stressing the power source. Also keep in mind how much wattage that will be so you get a resistor that can handle that amount of power. In the case of a 1A load the resistor will have to handle at least 5W.

Lets say I hook 25 meters of kanthal wire up to 220V AC with a resistance of 1.45ohms per meter, I use 25 meters of kanthal wire, that is 36.25ohms.

220 divided by 36.25 is around 6amps, my outlet is 7 amps, could be more.

Is 6 amps enough to heat the kanthal to 1000C (1832F)?

I don`t know how hot it gets at different amperages, is there a formula for that? Thanks

your wire has a resistance of 0.44 ohms/inch. If the maximum current from your 5 v supply is I amps, then the resistance you need is 5/I ohms, or 5/I/0.44 inches, or 5 x 2.54/I/.44 cm

design the element to have a resistance equal to the ratedvoutput voltage of the supply / the rated current. You don't need any other resistor