Diversity of insects is less likely to reach asymptotic mode even centuries later. Such a diverse organism has diverse array of body parts. Please share some material to make me understand about the varied parts in different orders.
The suggestions are excellent. I think that Beutel and Snodgrass may be a bit too complex for your level. I'd suggest that you start with Borror and DeLong's Introduction to the study of insects because it is easier to read. After you feel comfortable with the basics of insect morphology, you may move to more complex readings. There are many other books that you will find useful, for example, Imms' General textbook of Entomology (especially the first volume), Fundamentals of Entomology by Richard Elzinga, The Insects: structure and function by RF Chapman, and Encyclopedia of Entomology (four volumes, edited by John Capinera), among many others. You'll find that some topics are repeated in these books, but the focus is somewhat different and the details are presented in a slightly different way. They are quite popular, so probably you'll find them in the library of your institution or you may even buy them used on Internet.