First off, congrats you are making progress.
Second, yea you can reuse your old pistons so long as they are in good condition and provide the compression ratio you need to make the power you are after.
Next, you MUST look at the entire package to build reliable usable power levels; meaning in order to choose a cam you must have a plan that includes what intake you intend to use, what heads, what headers (size of primary tubes), compression ratio of the engine when built, type trans, potential gears, tire size, how you intend to use the vehicle (racing, cruising, etc).
The cam is arguably the heart of the engine but is reliant on all of the other systems to maximize it's potential.
Take a look at the stock specs for the cam (and engine in general), this will give you a base line. Next find the Direct Connection Race Bulletin for the A engine which will outline packages that factor in vehicle weight and provide specific parts. This will give you a better understanding of what parts work with what. There are literally thousands of combinations of possible parts if you factor in all of the various manufacturers and just as many opinions as to what works the best.
Think of it like a detective trying to solve a case; start with what you know and then begin to fill in the unknowns. What I mean here is, you know what engine you have, you know what the bore and stroke are. You need to determine if you are going to use the heads or get something new. Once you have these 2 issues resolved, you can then call any cam company and tell them what you have and what you want (in terms of power level) and they will tell you what cam will achieve that. Do not focus on any one manufacturer, look at as many as you can stand to. Look for packages that include the cam, lifters, etc and see if you can find something that interests you.
Point here is this, you can select X cam from Y company that is purported to deliver ZZZ HP, however if you do not have the heads (valves), exhaust and induction to compliment the cam you will not get what you are after. Additionally, if you do not have the right gears the power you will make will not deliver the driving experience you are wanting. If the gears are too tall (i.e. 2.76:1) it will run down the highway fine but not be pleasant to drive at lower speeds, consequently if the gears are too deep (i.e. 4.56:1) it will be a hoot up to about 45 mph when the engine is screaming.
Since you are planning on running a manual with OD, you have a lot of "wiggle" room on the gears, meaning you can get away with running something like 3.55:1 or 3.91:1 and still be able to cruise at 70 without much issue as well as do smoky burnouts in your driveway.
Induction is another thing you need to decide on; what intake and carb or EFI system. These need to match or compliment the cam, heads and exhaust.
If you are thinking "man this is getting complicated" you would be correct, however it is not as bad as it seems especially with the internet as a resource. DO NOT make any snap decisions on anything engine related, rather look at it holistically as a complete system and on paper put it all together and then do the research to determine if it all will work together. Keep in mind that because X cam works for someone does not mean it will work for you. This is not as daunting as it seems, you just need to make some decisions up front so that you can put the picture together.
I personally strongly recommend 3 things;
1. a roller cam
2. a timing chain tensioning system
3. a EFI system
Lastly, keep in mind that people have been slamming engines together for a very long time in everything from back yards to full up shops; it isn't rocket science but it can be done wrong obviously. A little research will go a very long way.
