我今年7-8月左右會去洛杉磯朋友既屋企...

i understand you will like to stay with your friend and family. that 's better than running around with the travel company.
your friend should take care you and take you for tour. that is what the friendship for.
if your friend can take the vacation in the same time. that will be great for both of you.
in one month, you can well soend half of time in LA area, then may go to SF or Las Vegas. it is good to travel alone or with friend. you can control your time, point to see and schedule.
July and Augest is kind of hot in LA. but the heat is acceptable ( it does not like HK's humid wet heat summer ),and the temperature will come down at the night time. most places, shops, home, car have AC. so not need to worry about.
one person, i think 1000-2000 USD is enough for a month lar. if you friend not going to charge you for stay...haha
no need to buy anything from HK, except maybe gifts to your friend and his family.

一個月對一個冇目的而去外國時間會比較長, 而且你係visit你個朋友, 佢自己都要返工啦, 陪得你幾多....不過我贊成你既想法, 人一定要去見識d新既野... 我同上面既睇法係一樣..2 個星期既 團已經足夠 (我明白你唔係太想跟團, 因為你會認為同番自己本土既人去, 好似感受唔到當地既生活文化..) , 係會有一定既唔同, 你可以中間離團, 再搵間motel仔住 三兩日. 真係好鍾意就住多一兩晚, 再番香港... 我係過來人, 我知有咩感覺~ .. 一兩個星期你會覺得好enjoy好好feel, 我都覺, 太長時間一個人係外國, 你會感到lonely, 同好無助....你英文好好又唔同 ...

如果你無目的咁去,選擇自由行好浪費時間同金錢架,你點解唔報團呢?雖然你慳左住宿,但只買機票都抵唔返,跟團其實都差唔多,仲有人介紹當地文化。如果你都係自己去,可以買本旅遊書參考下。