You can certainly use the Seachem line. Some may prefer this strategy for smaller, low light tanks. I think the Greg Watson ferts would be cheaper for most in the long run.
You ask if you need phosphate. Your tap water has a lot. I might be tempted to forego ordering the phosphate and test your water to see if your plants are phosphate hogs. If you do need phosphate you can always use a Fleet enema. I have been using the same enema for about 2 months and have lots left. Now, sources of K may be a bit harder to find locally. So you may wish to add some K2SO4 to your order so you have some on hand if you find you need to use it in the future. Currently I use KNO3 powder but am not adding any K2SO4, though I have some on hand.
So why not order some trace mix, KNO3, and K2SO4 in powder form.