Well, this will certainly be one of the major jobs you preform on you car. If you are asking for guidance I assume you have never done this before. If that is the case then like Elmer Fudd once said "be verwey, verwey careful"
Jumping past many things that you need to know I suggest you line up a well qualified welder that specializes in car restoration. I asked around my area of Washington State and found a guy that was used a lot by fellow hot rodders and they gave him high praise. After I spent the time and money to remove the old fenders and then fit up the new ones I was not going to risk all of that work by welding the new quarters myself. So I paid the guy $60.00 an hour for 10 hours to weld and grind my new quarters and I have to say that I was thrilled with his results. Once you decide who is going to do the welding you can also get their advice as to fitting the new quarters.
You also need to determine if you are going with new skins or complete quarters that include the C Pillar which fits into the rear window area. Depending on which repair panel you choose determines how you fit the fender.
Before installing the quarter skin---
After the skin was installed and primed-----
As far as replacing the inner fenders you will need to drill out the factory spot welds using a spot weld cutter that has a replaceable cutting head which you can find any auto body supply store. This is one tool I would not buy at Harbor Freight. My supplier gave me some good advice when he said 'use firm steady pressure but DO NOT put your body weight behind the drill' all that does is dull the bit quickly. His advise proved to be well founded for me. Remember you only have to cut through the first layer of sheet metal. You do not have to cut a hole in both pieces of sheet metal.
If you are just replacing the skin the you may want to use these clamps from Harbor Freight http://www.harborfreight.com/8-piece-butt-welding-clamps-44751.html I found them very handy.
There is so much more to tell but I am not the one to give that advice.
Be careful. Good Luck.
Im doing the same thing on my 74, but Ill give you my .02 on the research Ive found. Im cheap, so I will be doing all of the work myself, besides body filler and paint. I am also putting mini tubs in while Im in there. I have already cut my quarter panel out to expose how much I need to replace. For removing the old metal, I use a spot weld cutter from Northern and an Air Chisel from Waldo mart. It did the job pretty quick. My plan is to install the inner tubs, then the outer wheel houses, which are pretty much just plug welds. As for the quarter, I am going to cut the area out of the car where I will be putting the new quarter, keeping it as straight as possible. I will then Cleco the new skin over the area with about an inch or so overlap. From the inside of the trunk I will begin my first cut on the new quarter. Ive researched cutting disks and found a company who make a very thin disk. During my practice welding, I've found the thinnest gap makes for the better weld. This will ensure a perfect line. Once cut, I will peel back the overlapping metal and place a tac weld. I will place a tac weld about an inch apart until I make my way around the panel, while removing the clecos and overlapping metal. I will then go around the panel between the 1" welds, all the way around, then at 1/4" all the way around. After the 1/4" welds are made, I will place 3 quick tack welds to close any remaining gap. I will also quench the area with compressed air to keep things cool. For the welding I will be using Easy Grind wire, because im sure there will be a lot of that.
Thats my plan, but any advice would be great as well.
I have replaced both rear quarters and outer wheel houses on my 73. I would highly recommend using the butt weld clamps from HF or Eastwood. Measure measure and try to cut once. keeping proper gap is very important. If the panel is to close the weld will crack. Keep the heat to a min by welding at about 3" apart start at one end and go to the end and then start back at the beginning that will allow time to cool before you start again. Check out my build for pics. There are alot of guys that have done what you are starting don't be afraid to ask questions. Lots of knowledge plus someone that is a member here that lives in your area may be willing to stop by and help out.
Ventura 7 is absolutely right and I should have mentioned that using the Easy Grind wire makes a huge difference and it is worth the price of the wire. They call it Easy Grind because IT IS! I can't tell you how much work and heat you will save by using that wire. You should be able to buy it an any welding store but you cannot buy it at a retailer like Lowe's or Harbor Freight.
My EASY GRIND wire came in and I did a couple of practice butt welds. That stuff works great!! Even for a novice sheet metal person this would be a great idea as the weld grinds down MUCH easier. After grinding my practice welds I couldn't even tell where the seam was. Now just need to do all the fitting of the panels.