@wwarby
Welcome to A.org :-D
First off, how do I tell what Amiga I have?
If it's wedge-shaped with only two lights on the right (floppy and power) then it'll be an A500. The A600 has no numeric keypad. If it says "A1200" then it's one of them 8-) Desktop/tower Amigas should say the model on the front of them.
If I've got a shoddy old model, should I get a better one?
The A1200 is probably the most useful model (it can play AGA games) although you may run into trouble with very old games on it - nothing that cannot usually be worked around, though. An A4000 will be similar in the games it can play, but be far more expensive. An A500/600 should suffice for most older games.
Can I / Should I get a hard disk?
I've no idea how easy it is to fit a hard disk into an A500. An A1200 has space for a laptop-sized harddrive, although with care a full sized one can be added. This isn't needed for many old games (in fact, they won't often install without an extra program like WHDLoad) but is a must if you want to do anything a bit more serious.
Should I be able to run an Amiga through a TV using Scart?
Yep. For an A1200, get a composite (the yellow socket) to SCART converter. IIRC the A500 only has a monochrome composite output, so you'll need something that connects to the monitor output (you could use a modulator, although the quality is terrible and that wouldn't be SCART).
How about through a TFT monitor?
You probably won't be able to run games without something called a "scandoubler" - the Amiga's screen resolutions are at too low a refresh rate to work on monitors without a "TV in" otherwise.
What's the best screen solution
(Assuming that you mean "resolution") this isn't really an issue if you're only using games since they'll be using PAL/NTSC resolution. The most flexible display type is probably a "multiscan" monitor which can display TV signals as well as higher resolutions, although these are quite pricy.
Can you get any other new-fangled gadgets for an Amiga?
Sure - you can get PCI slots and a soundblaster if you're willing to pay for it :-D You won't really need anything else for playing classic games, however.
How about an optical mouse for example?
With the right converter, yes. Most optical mice seem to be USB nowadays, and while you can give your Amiga USB, it might not be worth it if you can find a decent non-USB mouse. Don't be tempted to plug an old PC serial mouse into the Amiga's game port though.
Is a second disk drive worth having?
They're great for games with multiple disks (e.g. the old LucasArts adventures, although many of these can be installed to a hard drive, which is even better).
What will it do for me if I get one?
You can prevent disk-swapping by installing games and apps, and it'll make the Amiga far nicer to use as a more serious machine.
How big?
You cannot use more than 4Gb without a much newer version of the OS, although you wouldn't need this unless you want to use the machine for what you'd use a PC for, IMO.
've read about there being a version 1.3 and a version 3 - how do I know which one I have
Turn on the Amiga and wait - it should say (if there's a hand holding a disk, it's an old version, if its a disk being inserted into a drive its newer).
how do I use it
Insert your "workbench disk" (if you can only find the master copy, make a backup ASAP). Wait a while for disk activity to stop, and you'll end up with a screen like any modern OS - double-click on icons to open them. Insert a disk (you can remove the WB one now) and it's icon will appear. AmigaOS menus are activated by holding down the right-mouse button and moving the mouse to the top of the screen. For instance, to rename a file, click it once, go to the "icon menu", "rename" (still holding down the right button) and then release it. Extra tools and utilities are held on the "Extras" disk. Note that you won't need WB if you're only using old games.
how do I upgrade
You'd need to open up the Amiga and insert new ROM chips. All your old games should work on 1.3, and if you've got an A1200 it'll have at least 3.0 which'll do fine. 3.1/3.0 (or at least 2.0) is fairly essential for serious stuff (e.g. with a harddrive).
Edited 11:18 UTC