GMATprep result is correct ?

You obviously took a diagnostic test, which is a very good idea. Look at the test and see what areas you need help with.

GMAT Prep should be a great indicator of how you will do with the prep level you are currently at. In your case, since you are starting out, you should not feel too concerned. I always encourage members not to take practise scores seriously. Try to learn from everything you do.

Measure your progress. There is a saying somewhere along the lines of... if you cant measure it, you cant improve it... which is a nice segue into a possible answer for your next question.

A long time frame does not guarantee too much. How will you know you are ready? Sure, you can go with a gut feel, but a more balance approach is again... measure your progress.

Please take the time to learn the basics first, no matter how boring it might be. I encourage you to only use authentic prep materials and then go experimenting with other prep materials. Stick with the OG and LSAT (for CR) for practice. If you can get your hands on OG 10th edition, use that material also.