How many times of urine it can absorb?

It depends on the volume of the baby’s urine.  Normally we recommend you to change the inserts once it’s wet and this is for hygiene purpose.

Do I need to buy extra inserts/liner/other item after I purchase the cloth diapers for additional features (if there is any)?

Usually for newborn you do no need extra absorbency. The original cloth diaper comes with 1 pc of new born and 1 pc of One Size Super Absorbency inserts. You can buy Overnite Fold-over insert if your baby is a heavy wetter or sleep long hours.
The flushable nappy liner does not add any absorbency.  You may use them as it’s to make the poo cleaning-up work easier by just flushing the nappy liner and poo down to the toilet
Is the cloth diaper thick?
Yes. The cloth diaper is a bit thick but this is for better absorbency and longer hour usage.
Will my baby feel dry wearing the cloth diaper made of  Softliner?
Yes. Softliner let the urine pass through to the soaker material (the insert) placed in the pocket of the diapers.The softliner will remain mostly dry.  
Can I put extra insert on the pocket diaper to be more absorbent? 
Yes, you can. That’s they beauty of Pocket diaper. You can customize the inserts. If your baby is a heavy wetter, then you can use the Overnite Fold-over inserts for night. Or else, the regular inserts made out of bamboo and microfiber is sufficient for the day.
For night use, how long it can last?
Should last you for 7-10 hours without change, with Overnite Fold-over insert. Comparatively, it should be equivalent to one Mamy Poko disposable diaper. You will need to change the baby in the morning.  However, if your baby does wake up in the mid night to drink milk, you may change the inserts for your baby in order to make your baby feel more comfortable. 
How long can the diaper last?
If you follow the wash and care instruction, it should last you more than 1 kid, meaning that if you cloth diaper your first child for 2 years, the same diaper can be worn for the following and following children.
How much urine flow per day?
An average newborn-6month: Baby wetting is 60-110ml during the day or at night.
Average 6month-1yrs: Baby wetting 110ml-140ml during the day and 143-182ml at night.
Average toddler wetting 130ml-160ml, during the day and 195-240ml at night.