1) Tk does'nt have an integrated spellchecker. You may be interested by PyEnchant.
2) 3) 4) is not that difficult (please forget my previous suggestion to use wxPython). You can pass a tag_config as 3rd arg of the insert method of the text widget. It defines the config of this selection.
See the following code which is adapted from the Scrolledtext example and effbot which the best reference about Tk.
"""
Some text
hello
"""
from Tkinter import *
from Tkconstants import RIGHT, LEFT, Y, BOTH
from tkFont import Font
from ScrolledText import ScrolledText
def example():
import __main__
from Tkconstants import END
stext = ScrolledText(bg='white', height=10)
stext.insert(END, __main__.__doc__)
f = Font(family="times", size=30, weight="bold")
stext.tag_config("font", font=f)
stext.insert(END, "Hello", "font")
stext.pack(fill=BOTH, side=LEFT, expand=True)
stext.focus_set()
stext.mainloop()
if __name__ == "__main__":
example()
