Thanks guys looks like i got lots of research to do and planning yet.
As Darrel says I would stick to the Tropica 'Easy' plants - particularly those rated for low light and low CO2 - it'll make your life a lot easier, and you can also try more difficult plants once your aquarium is established, if you fancy it.
For higher stem plants, personally I can recommend taking a look at Bacopa caroliniana, or for a really nice easy red plant Ludwigia Palustris, or for somehint a little more unusual Hygrophila polysperma sunset which has also grown very easily for me.
For the midground Cardamine Lyrata is a lovely delicate plant that has grown very easily for me, Bacopa Compact is also one that grows easily and low in lower light, and Staurogyne repens is a nice low bushy plant also, that is fairly undemanding. Crypts are a good option also if they fit with the design style you are going for - just expect to remove most of the leaves as they will melt to start with - I recommend planting them with a decent root tab, as mine have done really well on that basis, and have come back really bushy within a few weeks after their melt. Personally I'd always go with decent sized potted Crypts - I've had zero success with in-vitro Crypts. You might also want to check out Schismatoglottis prietoi - I got this recently, and it is a beautiful little plant - like a cross between an anubias and a bucephalandra, but can be planted in the substrate.
The foreground/carpet is more difficult is more difficult, though if you look in the 'Journals' sections there are a number of low tech tanks that have great carpets. Though my tank is high tech, the carpet is fairly heavily shaded in many parts, and I also didn't want to have be constantly trimming it, so I went with Marsilea Crenata. It takes some time to establish and mature, and grows slowly, but I really like the look of the mature dark green leaves, and it should suit a low tech tank.
Finally, as you have a fair few rocks, you might want to look at epiphyte species like anubias and bucephalandra species. For the anubias, you might want to go with smaller species with petite/mini/bonsai in the name, or Pangolino - the standard nana species can have quite large leaves, which might not work with the scale of your layout. On the bucephalandra species there are quite few to choose from, and they are beautiful plants, but pricey - but a decent quality pot will normally yield two decent small plants for you to place.
Also a couple of tips from mistakes I've made. Firstly stick to reputable plant suppliers like Aquarium Gardens, and Aquasabi etc - eBay sellers might appear better value, but they're not really, their plants are just smaller and lower quality. Also Tropica plants offer the highest quality in my view - certainly for in-vitro plants - so where there is a 'choice' in brands choose Tropica (or possibly Dennerle), with Aquafleur a close second for potted plants.
Secondly, the Tropica soil (which I have also) leaches a fair amount of ammonia in the first few weeks - I was seeing over 5ppm from the soil powder. If you are going to plant from day one before adding water, I'd recommend frequent large water changes (at least several per week) until the levels start to come down.
Finally, make sure you have your fertilizer regime sorted ready to start as soon as the plants are added. I'd personally recommend EI dosing - it's fairly straight forward, cost effective and easy to implement - you might need to look up whether the standard dosing needs adjustment for low tech tanks.