Jlien X
As for your recommendations, do you mean that I need more RAM IF I use just one drive (with everything in one partition)? I'm thinking of using an external drive for samples, projects, etc and in that case 8GB would be fine? (Well, my laptop can't accommodate more than 8GB RAM anyway...)

Whether or not you use a second drive, maxing out your RAM is definitely going to make life easier.
 
What I was trying to say about a second drive is that you really don't need one if you have enough RAM. I ran 8.5 on a 4-gig system with three drives and it worked fairly well as long as I didn't have more than a handful of tracks (up to 10 or so). That was a 32-bit Windows machine.
 
But, I took a second to go look up the specs on your laptop and I'd suggest you get something faster when you can. Your CPU is running at 2.1 gHz and, even though I saw on mention of this on the HP website, I suspect it's a 32-bit machine. When I ran a desktop with similar specs, I was running Sonar 8.5 and, as I mentioned above, about the best I could do was about 10 tracks with no more than a total of five or six effects on those ten tracks. So not every track could have an active effect. I got around that by freezing tracks when I was fairly confident they were finalized (although looking back now in light of my recent studies, I was totally naïve on THAT point) and/or bouncing each track as it was 'finalized' in order to cut down the load on the CPU.
 
So, with 47 tracks, you'll likely have to juggle a bit, weighing FX against CPU load in order to get them all to play at the same time. You may even have to mix a few tracks at a time, generate a WAV, mix a few more, generate another WAV, etc. then load all those mixed WAVs into a new project and mix from there. You know, do it the four-track-1972 way.  

mudgel
There is no gain by partitioning your drive in this way. In fact some would say that you've created more problems by doing this.

We always recommend 3 HDD but not 3 partitions.

Files invariably take up more space on disc than the actual file size. This Is due to the size of the blocks into which each HDD is divided. 2 different files can't use space in the same block so there is always some space left over in each block. When files are written to disc.

Well, on a laptop it can be quite difficult to use 3 HDD...:)
 
Partitionning introduces no overhead.  Yes you get less performances than with 2Hdd, but it's the same as having one disk with 1 partition and all your files on it. Partitions are great to separate datas from system files, in cases when reinstallation is necessary and HDD is not dead(don't have to waste time for backups,just reinstall system on C:). The gain of using multiple hdd is that they can be used at the same time. Since regular HDD are quite slow to access datas, you minimize the seek time overhead. That way having different disks for samples,system and sessions is great.
 
Concerning the post, a disk cleaning should prove to be useful (temp files can get pretty big). CCleaner is a good idea.
 
Another more "long term" option would definitely be to change your hdd for either a 500Gb or bigger. They are not that expansive (unless you have an old IDE slot which seems not to be the case with core2) and you'll be able to use a 100Gb or more partition for system which will be quite happy. Just check they are 7200rpm(WD Black are something like 60 euros for 500Gb-750Gb).
 
For external HDDs, firewire is a bit better that USB2. Another option is to get a USB3 or esata expresscard (cheap).Your core2 should have a slot for this.You'll then be able to get full hdd speed on external (my USB3 external HDD transfers 90Meg/s and it's a cheap one)
 
For SSDs on laptop, it's expansive if you need space and you won't be able to prevent wearing from system files writing(can't write them on a standard hdd).Also, you might get problems like freezes if your mainboard doesn't support SSD well (had this kind of problems). There's no way to know before you test it and it's a rather expansive test (if it doesn't work well, you will have bought an ssd which you'll have to use externally). External using expresscard is a better option. You can also use an SSHD for onboard hdd (not very expansive,but...Seagate ones are 5400rpm...it will be speedy for booting but it won't increase your playable tracks).