The drive will require digging out to a depth of 150 to 200mm below finished level. when digging out try to shave off the top levels if possible rather than pushing the spade into the ground, that way you will not disturb the sub base.
If you have to push the spade into the ground, then do not go too deep for the above reason.
With luck and of course depending on your type of soil, you will finish up with a nice flat surface undisturbed by digging the length and width of the proposed drive.
You could at this point hire a whacker plate which is a machine hired out from your local hire shop which has a flat vibrating base driven by a small petrol engine. You could be looking at around £30.00 per day.
I don't know what you intend to lay as a curb edgeing, but I would consider having one of some sort other wise you will end up with your loose gravel finish all over the rest of the adjacent garden.
Having got the excavating done, Yellow pages should find you a builders merchants such as Jewsons or Builders centre which are prety well nationwide.
Most will do a next day delivery and for the quantities you are going to require the delivery will be free.
The limestone chippings grade you require is colloquialy known as crush and run, this is 25mm to dust generally.
It is sold by the tonne, which is what the large white bags hold. The cost will be around £30.00 per tonne. Don't forget though when they are quoting you the prices will probably without vat unles you ask for with vat pricese.
Around where I live in South Yorkshire, the white bags are not on deposit any more and they become your property, but of course they are not free, the price is lost in the cost of the goods.
In theory, you get 10 sq. mtr of hard core per tonne at 100mm thick, but it is better to work on eight sq/tonne.
If when you have worked out how many tonnes you require, you start to shop around, and believe me, it is worh shopping around, ask for the price of a loose delivery.
You will find this is much cheaper and you will probably get more for your tonne than the equivalent number of bags. The cheapnes is of course because you are not buying the very nice white bags.
Use a line stretched between garage and road to lay your curbing straight and at the correct finnished height. You might find it easier if you purchase some rough wood 50*25mm approx,. and cut into 450mm lengths with a rough sawn point on one end. Along the length of the line, knock into the ground the prepared stakes so that they finnish with there tops at the taught line level and obviously in line with the line at both sides of the drive.
Across the width of the drive knock in further stakes to finish at the correct level with the side stakes. Get youself a straight piece of wood that will not bow when unsupported, say 100mm* 50mm. preferably the width of the drive or at least a couple of metres long. This with a spirit level will allow you to strike off from the side stakes across the drive and check
the levels of the intermediate stakes as you proceed.
When your hardcore arrives, if you have gone the bag route, ask the driver to use his hydraulic lifting arm to position each bag and the with a stanly knife slice through the bottom of the bag and let the hardcore spill out. In this way you will save yourself the chore of hand digging the hard core out of the several bags and barrowing into place along the drive.
If you have gone the cheaper loose fill route, you could ask the driver to tip onto the excavated drive but it will certainly over spill onto the adjacent garden and it will also be harder to shovel it up into a barrow off the soft earth, and you will have flattened some of your guide stakes in the process.
The road/causeway is a better bet if possible as this allows you to see how much you are laying and can adjust the infill height if you start a bit thin and realise you are going to have some left over, and if you have a bit too much, a negotiation with a neighbour could be made and again it's easier to barrow away from a hard surface than off the top of partly laid hardcore.
Either way you will need to barrow and rake out the loose hard core till it is equidistant up each stake. Once you are satisfied that the hardcore is laid equally along the length and width of the drive the stakes can be pulled out or if this proves difficult, knocked down to hard core level, there job done.
At this point the whacker plate comes into it own, this is noisy but quite theraputic, Ha Ha.
Over the compacted hardcore, lay some of the garden weed supressant cloth making sure that the sedges overlap each other. Some plain 100 or 150mm round headed nails can be driven through at intervals to hold the material in place.
You now have the choice of new gravel or the recoverd gravel from the rear. The recovered gravel is a temptation, but it will almost certainly be contaminated by soil. If you are going to reuse it, then it realy wants passing over a fine mesh grill that will allow the soil through and retain the gravel. This is a long slow proces, but if you don't do this, you will have weeds growing in no time. The new gravel can be bought from the same builders merchants as the hard core with the same proviso's as to price and delivery method applying. Quantities would be 20mtr sq, per tonne/bag. for 50mm depth approx.
The gravel wants to be about 50mm deep to give you a nice rakeable surface that can be kept in trim.