My new Smartphone... just what can I do -and what do I want to do- with it?? Locked?? Un-Locked?? S-ON?? S-OFF?? Rooted?? HBoot??

Nope, you dont have to be S-0ff to be rooted, only UN-locked.

You can do most all modifications with UN-lock EXCEPT go back to previous hboot & rom.

Recovery is separate from hboot. Recovery is a menu choice in hboot. A new recovery can only be installed if UN-locked or S-0ff.

3 do the S-0ff thing with Juopunutbear, being careful not to amend or skip any instructions in the S-0ff recipe (critical).
4 now your phone is s-0ff and locked. leave it just that way: no unlocks ever needed again and no pink warnings

I know it's counterintuitive, but if you unlock it again after s-0ff, even though it's s-0ff, you will have a nasty PINK Tampered flag every time you boot to hboot/custom recovery. And that crappy reminder stays even after you you relock. The Juopunutbear process relocks the phone, making it S-0ff, Locked. Perfect. Now with S-0ff, locked or unlocked doesn't matter regarding any roms or radios you may install and No warning flags.

Dont be intimidated by the wire procedure for s-0ff, just read it so many times beforehand that you effen KNOW it.

Rezound
AR Recovery 3.15
Stock hboot
ICS OTA
Rooted
SuperSU

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Rezound Developement?? Yup, HTC put a stop to that stuff with our phones. Even though the eng hboot is an official build the radio will brick your phone if it sees it on there with S-ON.

You said being S-ON with the ENG hboot will brick your phone right? So will running an RUU, which puts the phone back in S-ON, while on the ENG hboot brick my phone?
No. Running the RUU won't set you back to S-on. You'll still be S-off, but with a SHIP hboot (you'll notice also that the pink 'revolutionary' at the top of your hboot will be gone). Once you do that and are on the SHIP hboot with S-off, you'd need to do 'fastboot oem writesecureflag3' to get s-on again
Search for fastboot commands produced a lot!!
Fastboot Commands
another Fastboot Commands List
Gunnyman's quick and dirty adb/fastboot primer
Then a search for hboot commands produced:
[DEV INFO] Rezound HBOOT Fastboot Oem Commands
Please specify the extra commands and what they do would be much appreciated.
Also, do we flash this via Recovery or fastboot (with flash recovery option??)
A list of all the commands can be found here. To flash it you can rename it to PG86IMG and place it on your sdcard, then boot into the bootloader. Or, you can also flash through fastboot by using:
fastboot oem rebootRUU
fastboot flash zip PG86IMG_eng-hboot.zip
There really wouldn't be any plus to flashing this boot if I'm just an average Rom and Kernel Flasher right?
Doesn't matter if you're just an average flasher. Anytime you're flashing things to your phone, there's always a possibility to get into some trouble from a bad flash from a corrupt file or failed recovery or whatever. Having access to the extra fastboot commands can potentially get out of a jam. Sometimes fastboot can be the only way to communicate with the phone, and in a situation like that, you'd prefer to have as many available commands as possible. You could find a fix for your whatever problem you're having, but the command may not be available unless you're on ENG hboot, and that would suck if you weren't.

Acronym, Definition. OTG, On-The-Go (USB 2.0 specification).
Android Open Kang Project - AOKP.

Android Geeks Android 4.0.4 Update
Juopunutbear S-OFF
Juopunutbear

Android Info
More HTC Android Info
TWRP (Team Win Recovery Project)

Android Forums
-boot to bootloader: pull the battery,power on into hboot via power/vol down. select fastboot from the hboot menu. plug in the phone.

-check for connectivity:

fastboot devices

-should return serial number

-enter this command to get us some info about your phone:

fastboot getvar all

tell us what the main version number is(or copy/paste all the info)

-temporarily launch your recovery to phone memory:

fastboot boot <recoveryname>.img

again,if youre using amon:
fastboot boot recovery-ra-vigor-3.15-gnm.img

-youll see a (really fast) green status bar on the top right as your PC sends the recovery to your phone. youll then see the HTC splash screen,then your recovery.

now that youre recovery is running,you have lots of options. you can mountusb storage to move things on and off the sd card without having to move it from one phone to another. you can also flash the main version tool recomended by obscuro: main version tool (wich i would strongly reccomend)

at this point,if you have a stock backup you could restore it. or you can relfash your rom. with your recovery booted in this manner,it is able to write the kernels,so a backup should restore fine,and if the rom is scriped to flash the kernel(most are,unless they are old) it will flash fine.

again,as long as recovery is launched from fastboot like above,you dont need to flash kernels seperately.

once you are sorted,and bck to a working phone,id strongly recomend to permantly install amon in place of cwm. you can do this just like above,except use this command to permantly flash amon:

fastboot flash recovery <recoveryname>.img

for amon:
fastboot flash recovery recovery-ra-vigor-3.15-gnm.img