harlo Mac Warriors
I have some questions to ask
1. The new OS is free upgrade but I'm using ver 10.5.8 how to upgrade since i dont have an "App Store" for this OS. My current macbook is 4years old wor. WIll it be slow after upgrade?
The official answer is approach the Apple Store fellas and have them help you on this. This article will answer some of your questions
How to install Mavericks over Leopard | Macworld
2. With regards to the latest 13-inch: 2.4GHz with Retina display. I noticed that only the highest end of the 13" is able to upgrade the HDD storage from 512 to 1TB options. But the first 2 basic version (fixed at 128GB and 256GB) cannot wor. My question is am I able to do the HDD upgrade on my own in future when the HDD price come down?
The answer is most likely NO, unless the PCI-E board of the SSD storage is removable. Wouldn't know until someone start dissembling the latest MBP series. You are encouraged to get the SSD size as you anticipated to be adequate for your daily needs. If you need more, offload to an external USB3.0 drive or a NAS
3. RAM question: 8MB ok or going for 16MB? I'm mainly normal user and do some Photoshop as well as video for wedding at times only
8MB or 16MB will not serve your needs. 8GB or 16GB will be more reasonable

Basically 8GB can carry you far. 16GB is a tad too much for most consumer, however, if you can afford it, why not. I'm using a 17" 2009 MBP series and is on 8GB and have been doing numerous photo editing tasks on both CS5 and Lightroom 5. Memory is often not the reason why you get slow down at 4GB and above. It's often your disk and your computing power if you feel slow in some filter stuffs.
For video editing, memory will be your biggest issue, computing power is. If you can afford a Mac Pro, go ahead. If not, live with lower expectation and don't edit a 4K video.
4. In terms of Processor which one is better performance?
4.1 MacBook Pro 13-inch without Retina display 2.9GHz Dual-core Intel Core i7, Turbo Boost up to 3.6GHz [Add S$ 210.00]
4.2 MacBook Pro 13-inch with Retina display 2.8GHz Dual-core Intel Core i7, Turbo Boost up to 3.3GHz [Add S$ 420.00]
--> one is 4th gen the other is higher processor speed
5. Qua-core Intel (15" model) is alot faster than Dual-core (13" model)?
Thank in advance! =)
Certainly for the kind of tasks you have in place, Retina display will give you more screen assets for editing. Between 2.8 and 2.9Ghz, doesn't make much of a difference. Turbo boost will most likely not kick in if you are already using multicores intensively by your application.
Quad-core will be faster if your application uses all the cores, which you will most likely be using for video and photo editing.