Forged pistons are generally more for race applications and, naturally, more expensive. Not out of the ballpark more, but there is usually a couple hundred bucks difference. Hypereutectic pistons are sorta the 'middle of the road' - not really suitable for all out race applications, but will work for occassional racing. More expensive than stock pistons, not as expensive as forged. I'm running Keith Black hypereutectic pistons in my 392" stroker from RDI, as installed at Olthoff's Racing. I run my car at track events, but no wheel-to-wheel all out racing. I'm confident the hypereutectics will hold up to my driving style with no problems.
ARP con rod bolts are definitely what you want. Superb quality for just a few bucks more - isn't everything always "...just a few bucks more"?
Oversize pistons are usually marked somewhere....but you need to know the 'code'. I've seen some marked as '+1' meaning they were for cylinders that were bored .010" over...'+2' for .020" over, and so on. And, I've seen some marked '+.010', too...just depends on the manufacturer, I'm thinking. But, your parts guys should be able to help. If your block is standard bore, and not been over size bored to clean it up or anything like that, I'd just mic the currently installed pistons, and match up the new ones. I seem to recall you need at least .020" difference in the cylinder bore and piston size...more for aluminum pistons as they expand more when heated.
Be sure and send your rotating assembly...crank, rods, pistons, etc. ... to the machine shop for balancing and blueprinting, and not just assume it all balances. The cost is worth the performance. It really makes a difference in the finished product.
I'm sure someone else with more experience than I will weigh in on your questions, too. And your machine shop will have MUCH more experience, too, so use them as a resource as well.
Good luck, and let us know how it all turns out.