Q1: is RAID 0 setting should use a the same HDD or can I just use different kind of HDD?
A RAID array can have any types of drives; but you will get the best performance if the drives are identical.
Q2: should raid 0 be set first before installing the OS?
Yes, your array has to be created before you can install an O/S on it.
Q3: if a SSD and a 1TB HDD set as raid 0, is the R/W speed run as SSD speed?
No. A RAID-0 array's Read/Write performance is based upon the drive in the array with the slowest
Read/Write speeds; so if you mix an SSD and a HDD in the same array you are not using the SSD for the reason you bought it -- speed.
Also a RAID-0's total capacity is based upon the drive in the array with the smallest
So if you RAID-0 a 128GB drive and a 1TB drive your array's total capacity (before formatting) would be 256GB.
Q4: how if used a two the same SSD and set it to raid 0, is the speed runs almost double?
results will be close to double. In real-world use you probably won't notice the difference between 2 SSD's in RAID-0 and just using them as separate drives.
The exception where I would recommend SSDs in RAID-0 is if the drive sizes are small.
I would recommend 2 64GB SSDs in RAID-0.