First of all, if the system has been leaking, you will need to have it vacuumed down and leak tested prior to refilling the system with gas. From you comment about being new to air con i suspect that firstly this will be news to you and secondly you won't have the equipment to do it or know how to use said equipment.
With this in mind, i would suggest the following :
Do what you can in terms of fitting new parts but don't fit the new dryer yet. Find a good air con specialist (not the likes of Fik Wit and similar "high street" places") that knows what they're actually doing, phone up and explain you've had a leak, the system emptied itself and you've replaced the leaky pipe so you need it vacuumed down, leak tested and then regassed with new oil and leak dye.
That way the specialist can advise you of the costs of the individual parts of the procedure and the total cost of the new oil (it's mainly the compressor that needs the oil, you don't want that contaminating the silica crystals in the dryer!
), leak detector dye and importantly, the gas.
As i'm sure you'll agree, there's no point regassing it if you haven't got it leak-free, only way to be sure is to vac it down and leak test it. If all is well then, the dryer can be fitted (again, no point opening the new dryer until you know the system is leak-free), vac down again, add oil, leak-dye and gas and get it working again.
One important safety tip - no smoking while working on the system!
Some refrigerants can react with tobacco smoke to creat cyanide gas. It could be an old wives tale but i've never fancied putting it to the test! You may think the system is empty but it won't be truly empty until it is vacuumed down to nothing.