Fuse holder : the terminals are MTA Uni F630 although I suspect other manufactures make them as well ( Bosch?, TE? ). I got mine from Polevolt
Terminals for Fuse Boxes: Polevolt Ltd
Item 3-7921/10 is good for 2.5mm² cable.
( This reminds me that I need to get some more - thanks )
No. If you're using the large square relay holder typical of the 916 ( as you can see in my pictures ), you need 'TE Positive Lock' and 'TE Standard Power Timer ' terminals. Both of these are a lot easier to find than the fuse holder terminals.
e.g. Farnell for the positive lock 0-0927855-6 - TE CONNECTIVITY / AMP - CONTACT, POSITIVE LOCK, 1-2.5MM | Farnell element14
and for the power timer
| Farnell element14
You'll need to use at least 2.5mm² wire for the HRW supply so make sure the power terminals have that capacity! The relay coil terminals only need 1mm².
If you have an RS ( Radio Spares ) counter near you, use them. They may not have the exact same part number but they will have equivalents and get them delivered to the store/counter and pick them up for free.
If you're using the compact relay holder as found in some locations of Phase 2/3 cars then the terminals are 'Positive Lock' and 'junior power timer'.
Be careful separating the halves of the relay and fuse holders. They do take take some careful separating and the fuse holders are especially fiddly.
G404? That's a good plan and realistically you can use the same fuse ( saves adding an additional fuse holder ) because, as you point out, the two loads will never be using the supply at the same time.
For the relay coil, I'd pick up the HRW circuit at connector G73. On my car this is tucked away at the base of the driver's 'A' pillar. In fact, on my car G73 is 3 connectors ( G73a, G73b and a totally undocumented one I call G73c. Phase 2/3 cars have G73a,b, and c whilst early phase 1 cars have just G73a and G73b ( I think ). Some cars have G73 in the passenger footwell. You'll need to find yours!
If you do tap into the HRW wiring at G73, you'll need some 1mm² wire to run from there to your new relay and the suitable terminal. That will either be male or female ( I can't remember which way round the connector blocks are ) TE Superseal 1.5mm male or female. Typical TE part numbers are 282110-1 and 183024-1.
Hopefully 'm not trying to teach you things you already know, but I have a bit on crimping terminals ( with and without pliers ) here
Those Laser crimping pliers are OK but are not ideally suited to the smaller terminals. I've subvsequently bought some of these
which do a better job with the smaller terminals.
Hope that helps.