Nothing wrong with sand in a planted tank (I use it in mine) but like spook says sand is inert, It will hold no nutritional value for the roots of your plants to use.
Luckily for plants they will adapt to take all the nutrients they need from the water column.
Having a substrate that can hold nutrients will help plant growth but its not the be all and end all that people make out.
If you stick with the sand you can use "root tabs" to add nutrients to the substrate if you wish.
Or for the cheapest option possible you can use certain cat litters. (but the right one must be used as there not all the same)
This is a well known one that works very well, you just have to make sure you wash it extreamely well before putting it in your tank.
http://www.tesco.com/groceries/Product/Details/?id=265235247
As for liquid carbon, you have to be a bit care full with it.
Some plants and fish will not tolerate it and if constantly used will kill them. (it is poisonous to aquatic life)
Signs in plants are easy to see as they will start to melt. (go brown and mushy)
signs in fish can be different depending on species but normally erratic swimming, gasping, redness to the gills, are signs they maybe having trouble with it.
Most fish will tolerate it in small doses though but a massive overdose could wipe out your entire tank.
Cost for you will be high though, from the link £7.99 for 500ml.
5ml a day is a bit optimistic though if you only have a few plants maybe ok.
For comparison I have a 200l moderately planted tank and dose 25ml of glute a day, thats the absolute maximum I can dose before signs of fish stress.
As for ferts you would be much better off EI dosing, not only for efficiency but also cost.
This is a very good starter kit with a video on how to use it.
http://www.aquariumplantfood.co.uk/fertilisers/dry-chemicals/starter-kits/ei-starter-kit.html
For flow normally a spray bar the entire length of the tank at the surface facing the front panel is the best orientation for good flow. (straight tanks, curved tanks can be a nightmare)
If your getting a build up thats a sure sign you have a dead spot in the tank.
A single power head in the middle of the tank near the top pointing directly at the front will provide pretty good flow.
Make sure you get a power head suitable for the size of your tank.
A good thing for lighting is to use plug socket timers, make life easier for you.
And as spook says if you go for injecting co2 put the solenoid on a timer. Plants dont photosynthesize when there is no light so no point wasting gas when the lights are off.