Before even thinking of SSDs, I'd add more RAM. 512MB is very little for a modern operating system to work in before you add a DAW on top. On a DAW you want to avoid Windows writing to the swapfile on the disk as much as possible because it takes time and that time often means dropouts.
As for SSDs, unless the laptop has a SATA interface built in then SSDs are pretty pointless as the drive interface itself will be a limiting factor in data transfer.
In a new build, personally I'd go with Intel rather than AMD for the cpu and motherboard chipset. I'd also price in a good cpu cooler and quiet fan and a quiet case fan - Noctua for example. Seasonic make good fanless power supplies though they aren't the cheapest on the market. Unfortunately for any computer component that generates heat the easiest and cheapest way to get rid of it is a cheap, noisy high speed fan so that's what you'll generally find on cheaper components.
As for graphics, the Intel on-chip graphics are OK but can be a bit slow even for dragging windows around the desktop. If your budget stretches to it I'd look for a low price fanless gpu. Doesn't have to be too powerful, and there are quite a few around if you look for them. Sapphire make AMD-based fanless boards at pretty good prices and some are quite capable - my DAW has a fanless Sapphire AMD R7 200 series gpu in it that can even cope with less stressful 3D games without problems.
As for operating system, 64 bit Windows 8.1 is where I'd go. having run Vista, 7, 8 and 8.1 on a DAW I'd say each release has got a bit better at handling real-time audio processing and generally a bit smoother, faster and lighter.
SSDs make sense as the system drive in a new build because they speed up access to data considerably. Also maybe for storing samples. As for spooling audio to and from, they are also good at this but the frequent writes may shorten their life (I can live with that, others differ - my current Intel SSDs have been in use 2 years and show no sign of slowing down yet). If you only want to use a single SSD then use it for Windows and applications and a big 7,200rpm HDD for everything else. Avoid the "green" drives which save power by varying their rotation speed, they are fine for many purposes but not for streaming multi-channel audio. Partition the HDD so that the first partition is half or less of the total capacity then use it for Sonar projects (the first partition is nearest the outer edge of the disk which means better sustained read/write rates). Use the rest for the documents, pictures etc. directories that Windows requires (you can move them from their default location on C:) and anything else you need to store.