It sounds like you've got a decent combination worked out for a strong street performer. That engine should easily be capable of the horsepower goals you've set. Your concerns over the strength of the stock internals are wise, but not completely necessary. First of all, the stock cast crankshaft, provided it is in the condition GM intended, should be no problem. The two-bolt-main block is also pretty much a non-issue. Four-bolt blocks are appealing, but many race-engine builders will point out that the extra bolt holes drilled into the block webbing can actually weaken it. Either way, the power output and usage you describe shouldn't challenge either type of stock block. For a little added insurance at a relatively low cost, use a quality main-stud kit such as those offered by ARP. The stock rods will likely also work just fine, but make sure to have them reconditioned by someone with skills. Grinding the parting lines off the beams, shot-peening the rods, and resizing them after fitting high-performance fasteners (also offered by ARP) should produce plenty strong rods for the application.
Note that not all Chevy factory rods are created equal-some are more substantial than others. Some heavy-duty truck engines have beefier rods than your two-bolt passenger-car mill probably ran, and of course, there are the famous "pink" rods as found in early LT1 engines. A relatively low-cost alternative might be a set of the new powdered metal rods used in '90s-era LT1 Gen II small-blocks. Although traditionalists may balk at their unconventional construction (actual metal powder formed into a con rod under extreme pressure), these rods are said to be more durable than pink-type rods, and are usually priced around $200 a set, brand new.
As for pistons, a set of high-quality hypereutectics should work well for what you want, provided you don't intend to add a significant amount of nitrous or forced induction later on. Even with hypereutectics, reasonable nitrous hits (100-150 hp) and boost levels (under 10 psi) are usually all right provided the tuning is accurate throughout the rpm range. When you select the pistons, go for a performance-oriented design, as opposed to a "rebuilder" type. The obvious reason is the increased durability, but many pistons intended as stock replacements are designed with a lower compression height to compensate for combustion-chamber volume lost by cylinder-head and block-deck resurfacing. This means lower compression, which you don't want. A good flattop designed for near-zero deck-height will serve you well.
A final note on the building of the engine: When it comes to street/strip type engines, the potential for failure will very often be more contingent upon the quality of the machine and assembly work than the strength of the parts being used. Select an established shop that is versed in performance/racing engines, and make sure the machinist understands what you want. You obviously don't want slapdash work from the local taxi-engine rebuilder, but you also don't need someone talking you into a billet crank and a Bow Tie block for your street engine.
On the rev kit, the answer is yes, they do seem to work as intended to limit valvetrain chaos without resorting to insane valvespring rates. However, they are typically used in applications that see higher rpm than yours will, as well as those using more radical cam profiles, particularly ones with "fast" ramp angles. The valve float you experienced in the past was most likely the result of an engine in need of new or better valvesprings. Your engine should do fine with typical performance valvesprings like the ones your AFR heads should already have. When in doubt, ask the cam manufacturer for a recommendation.