Best Kind of decking materials and fasteners to use?

by JW
(PA)

I'm replacing 5/4 x 6 Western Red Cedar / Patio Grade / Select Knotty / S4SRE Radius Edge with the same type of material (not slotted).

The original PT (CCA-C) joists, beams, posts, connected ledger,galvanized hangers/connectors/nails are in good condition. The deck was built in 1994. It is located in Central PA (near Harrisburg).
The original decking was 1/4" spaced & faced screwed (90 degrees)with what appear to be sheet rock Phillips bugle heads. 60% of these screws cannot be removed intact with just a standard bit, screw driver or vice grip. They usually sheer or torque off when you rotate them, leaving an inch of shaft stuck in the joists.

My questions are:
1. What kind of fasteners should I use for the new replacement decking?

I'm leaning toward using one of the hidden fastener systems, but wonder if face installed stainless steel screws with WRC plugs would be any easier, cheaper or faster to install?

Has anyone used a 45 degree jig to edge set the deck screws with long term good results (i.e. 2 screws edge set @45 degrees/ 1 screw @ board edge / joist)?

Which clip systems have you used with good results (i.e. Lexan, stainless steel, polycarbonate etc.)? Is it worth slotting the board edges to use the biscuit type fasteners, or would the screw & prong types (i.e. Tiger Claw TC-2S) be better?

2. What gap or spacing should I use between boards? Original 1/4" spacing trapped a lot of leaf, twig, dirt debris- enough to support moss growth (deck is under dense tree canopy), which rotted out board edges. Should I consider going to 5/16"?

3. Should I consider using joists protectors; or deck spacers (i.e. Grace Vycor Deck Protector; Simpson Strong-Tie)or are they just gimmicks?

4. What clear UV / water penetrating sealers have you tried or like?
(i.e. Penofin Aquafin® Waterborne Formula, Cedarcide CedarShield, Flood CWV-UV/UV5/deck & spa,Sikkens, Ready Seal, DEFY Hardwood Stain, Thompson's etc.)?