《葛传槼英语写作》两个句子的理解问题

《葛传槼英语写作》两个句子的理解问题
在序言里葛老说了这样两段话：
1、Such a book ought to give such principles and rules； only as are based upon the actual practice of good authors． Some of those found in nearly every popular manual of position serve no definite purposes and therefore prove to be only so many handicaps in the path of the writer of English,who has enough to take care of without the interference of those unnecessary “technical” restrictions．
2、No book can teach anything to careless students or to those who feel little or no interest in the subject． Nor is it advisable to take too much for granted in Chinese students of English,who are necessarily supposed to have made progress in their studies with the help of dictionary and grammar．
一、在第一段中,;"who has enough to take care of without……“这句话里,
（1）enough什么?
（2）take care of的又是什么,
（3）the writer of English指的是不是“用英语写作的作家”?
（4）为什么说是说so many handicaps in the path of the writer of English?用英语写作的作家难道也会有那么多的handicaps么?
（5）Some of those found in nearly every popular manual of position serve no definite purposes and therefore prove to be only so many handicaps in the path of the writer of English,who has enough to take care of without the interference of those unnecessary “technical” restrictions．这句话几乎不能理解,即使都把意思查了出来.
二、第二段中,我能理解作者葛老是把“take Chinese students of English who are necessarily supposed to have made progress in their studies with the help of dictionary and grammar too much for granted"给变化得更平衡了,可是不能理解：
in Chinese students of English中的 in 有何用?