Respraying a car.

Preporation is the key mate make sure your prep work is spot on, wet flat your primer with 600 and block it where you can to make it as flat as possible, then a light scotch off with a fine (grey) scotch pad, obviously masking it up is also is a tedious job but spend the time doing it right.

When your ready to paint, panel wipe the car with a lint free cloth then use a tack rag, mix your paint 50/50 and apply a dust coat 2-3 times don't try and get a good finish at this stage, allow a flash off (20 mins) if warm, then hit it with two heavy coats, leave it for a few days then block it wet (plenty of fairy up liquid) with 1200 wet and dry then re mask if need be (advisable)

Then give the car another 4-5 coats you will get dry patches with cellulose but don't worry to much, and letting it go off for a few days and re-doing it may sound a pain, but again with cellulose to get the best finish it is recommended

Again let it go off for a few days then use 2000 wet and dry on the block again plenty of fairy and flat it to a silk peel free finish, then use farrecla g6 rapid on a polishing mop if poss, or by hand until she shines

Some pics may be helpful to assist you more

No just primer your repair areas, then if the rest of the paint is in good condition just wet scotch pad it to key it up and that will be fine.

Doing a panel or a few at a time will be easier and more achievable imo.

if it is really warm then up the thinners but cellulose isn't as thick as it used to be so i would say start at 50%

If you haven't sprayed before then stick to 50/50. If you're then feeling confident thin the celly further for the final coat.

Best of luck - oh, and we want to see the pics when you're done.

i'd be very suprised if you get good coverage with just 2 litres. I would have said 3 would be a bare minimum to do a smallish car. That aldi compressor looks ok for the money. you do get what you pay for with compressors. Going on your budget theme I use one of these hvlp guns
www.ebay.co.uk/itm/Mini-Jet-HVLP-Gravity-Spray-Gun-Smart-Repair-Twin-Pack-Blue-and-Silver-Set-/220914515313?pt=UK_Body_Shop_Supplies_Paint&hash=item336f87fd71

Use it mostly for refinishing wheels, but have used it to spray an mx5 hardtop, spoiler, front wing etc. Finish has been pretty good, most people don't realise that I had sprayed any of the parts.
If your painting gloss, use high gloss thinners, gives a much nicer finish that std thinners. keep the std thinners for primer, satin and matte finishes

Agree with A to the K, 2l is a bit stingy to be honest. If it's your first real stab you'll waste a fair bit cocking around with practice runs too.

Well I want the car to look the business and that why I asked the question in the first place. It would be daft not to take the advice so I'll order the same amount of paint again and mix both into one

Doing a panel at a time would be the only thing that aldi's compressor could manage,doesnt have enough cfm or tank capacity for a full respray.....couldnt you hire a bigger one??

would have to agree 2lt isn't enough it will look patchy where you have areas in primer if you can't get any more paint then blend them in with some rattle cans. I used 5lt silver and 5lt lacquer on my Gamma when l painted that and to be honest could have done with a few more coats of lacquer, but in the end after flattening it back and polishing it up (all by hand!) l was very pleased with the result. Luckily l did have the use of a mate's spay booth and l bought a good gravity fed gun.
Like others have said preparation is everything, get rid of any polish on the car with something like white spirit, key the paint underneath, if you've got Sharp edges put a few coats on them first so you don't polish the edges back to the paint underneath.

Good luck

If you have the time take as much off the car as you can, trim, handles etc. No matter how good you are at masking it always looks better with things removed.

If you buy some more paint just pour it all into one big tin and mix it well to avoid the shade difference issue.

As has been said above preparation is the key. Cellulose is pretty forgiving to use as you can put loads of coats on, flat and polish it etc but it does show up any imperfections so good preparation is vital.