Hi!

First, great deal!  I had a hard time resisting spending more money than I did there, at the end I tried to get @LoadWB to spend his money, instead, which was great fun.    The A500HD+ is one of the best-performing, and most "esthetically pleasing" hard drive controllers available for the A500, IMHO.

Second, you don't show it in your picture, but you did get the external power supply, correct?  While it's possible to run the A500HD+ off the 86-pin port only, which is what I do, it's not recommended to do this unless you have a low-power drive or one of the SCSI-to-CF or SCSI-to-SD solutions, so as not to tax the bus and stock PSU too much.  Just mentioning it to verify that you're not having a power problem.  http://members.iinet.net.au/~davem2/overclock/a500hd.html

Third, there are pretty much more different options for what you can do with this setup than there are clouds in the sky.  If it were me building another A500 system, here's what I'd do:

Get a new 3.1 ROM ($17 at AmigaKit):
http://amigakit.leamancomputing.com/catalog/product_info.php?products_id=157

Get a set of 3.1 disks ($16.34 at AmigaKit) and do a fresh format & install of Workbench 3.1:
http://amigakit.leamancomputing.com/catalog/product_info.php?products_id=1211

Upgrade to a 68010 processor (good for about a 5% speed increase and allows you to use the "Quit" key in WHDLoad, usually run about $5-$10 on ebay):
http://www.ebay.com/sch/i.html?_odkw=motorola+68010&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.TRS0&_nkw=motorola+68010&_sacat=0

Upgrade to an ECS Denise (optional, but I like to have it personally):
http://www.ebay.com/itm/Amiga-Super-Denise-8373-NOS-for-Amiga-500-2000-and-3000-/161756512645?pt=LH_DefaultDomain_0&hash=item25a9708185

You already have plenty of fast ram in the sidecar, looks like yours is already maxed out, if not you can put up to 8MB in there with standard 30-pin SIMM's (also usually run around $5 each on ebay).

If you only have 512K of chip ram you should look into the mod to upgrade it to 1MB.  This is pretty easy on most variants of A500 motherboard, instructions vary depending on which MB version you have and which Agnus.

If you still want to keep fallback ability for 1.3, you could get a ROM switcher.

...in any case, a 3.1-equipped, 68010 A500, with 1MB chip and 8MB fast is plenty sufficient for tinkering with Workbench (you might look into the "BetterWB" pack), and also for playing just about any classic game available through WHDLoad.  Obviously some folks might prefer to forgo all those upgrades and just use a Gotek or HxC variety of floppy emulator, not my personal cup of tea, but "as many options as there are fish in the sea", and all that.  Good luck, have fun, here's a couple more links to get you started:

http://lilliput.amiga-projects.net/BetterWB.htm

https://en.wikipedia.org/wiki/WHDLoad

http://whdload.de/

If you really want to max it out, get an Indivision ECS (usually around $100), which will allow you to use any modern monitor.  I love 'em, but again that's just IMHO, some people prefer the classic CRT's, blech!  :p

It seems to be the same GVP drive I use with my Amiga A500 Plus with Kickstart 2.04. I didn't get any documentation , the original HDD in the unit soon failed, then I had to fit it with a new drive which already had Workbench 2.x and some software installed. There's a topic I posted about it somewhere on here. I've never heard anything about powering it from the A500/A500 Plus though. It has its own PSU, which I switch on first, then allow it to spin up before turning on the A500 Plus. When I turn off the HDD PSU the Amiga A500 Plus screen goes blank, although it's still in the same colour scheme as before.

My GVP drive has some extra RAM, but not the maximum. If I got any more RAM, it probably wouldn't work with the RAM I've already got. I recently noticed an interface on the back of this unit, but I don't know what it's for. Would this allow me to fit a CD-ROM drive of the right type with the right cable? I don't know.

Of course, the classic CRT monitors are best for the Amiga, except for hires productivity display modes, as pointed out by Kooky Tech (Dan Wood).

I have same hardware wich is powered through A500. It has a 4gb HP hard drive and I haven't had any problems.

Once again, Oldsmobile_Mike has swung to the rescue with a ton of well-written, helpful advice and links!

A follow-up question (which may warrant its own thread, if the answer is complex): a few years ago I purchased an "Amiga Forever!" CD which contains various emulators, ROM's, OS's, etc. - does that mean I could legally request someone make me a set of OS 3.1 floppies, or do I still need to purchase them the normal way?

Thanks again - I'm so grateful for all the help here!

Yes , because you have Amiga and it has kicktstarts and it came with
Workbench.If they got lost I would say nobody will give you legal problems but you can still try and contact some people if you want some (problems)

@AmigaBruno -

You kill me, man.  Don't just say you can't do it, thousands of people have done it before you.  Research man, research!

To plug into a 500 sidecar all you need is a SCSI cable an an external chassis to physically hold and power the drive.  I bought mine off ebay a couple years ago for $3 from some Mac user.  

The physical connection is easy, configuring the SCSI ID and termination is what's hard, if you've never done them before.  Also I recommend OS3.1 or 3.9.  No reason you couldn't do it with an earlier version - again - you'd just be making more work for yourself, doing it that way.

I'm a very visual person, I can learn more from a few pictures than I could from a thousand pages of text.  So if you're like me, here's a few pictures to get you started:

Do not want to hijack this thread, however was following it as I have a similar HD8+ and have a quick question on the ROM chip ... so buying the ROM chip offered on ebay is not enough? You also need an additional board?

The 4.15 ROM chip off ebay will plug right in.  It's the GuruROM which requires a PCB adapter fitted between the ROM chip and the socket.

Edit:  Pic 1, regular ROM.  Pic 2, GuruROM.