Christmas Ale advice

[OldAl]

I'm planning a strong old ale for this Christmas (bltn) & I need some advice please.
I'm looking at 4 gallons(English) (18l) at an OG of around 1075, but not too sweet.
Pale colour, well hopped with a hint of orange & spice.
I'm using the DL recipe for Celebration Ale as a basis (p242 TheBBoB), adjusted for 80% efficiency.
Here's what I've got so far:-

10lb (4540gm) MO pale malt
1lb 6oz (600gm) flaked rice
6oz (170gm) crystal malt
Barley-wine type water
90 min mash
6oz (170gm) wheat malt (got some spraymalt that's hanging around)
8oz (227gm) demerara sugar
8oz (227gm) white sugar
3 1/2oz (100gm) Bobek (5.2AA) at start of boil
1/2oz (15gm) Amarillo (9.1AA) after 75 mins
1tsp (3gm) Irish Moss after 75 mins
1/2oz (15gm) Amarillo (9.1AA) at end of boil
Pared rind of 1 large orange at end of boil
90 min boil
Nottingham yeast 2x11gm

DL suggested a mash at 148F (64.4C) & to stop sparging when the wort hits a certain SG,
but I want to mash with the complete brew length + a bit extra (say 5 galls 23l),
use just the runnings for the wort, & all the spargings to make a shandy (say 3 1/2galls, 16l).
Is this feasible?
I know there are better options :-
(eg a full 5 gall old ale & a separate 5 gall light bitter for the shandy,
or better still forget about the shandy & brew a full-bodied 5 gall bitter or lager)
but I'd like to try it this way.

1. Pale malt is 76% of fermentables - is 10lb enough?
2. This will be a very thin mash, should I adjust the mash temp (148F 64.4C) either way?
3. Will using Amarillo as the only hop (say 2 1/2oz to replace 3 1/2oz Bobek)
give an overpowering orange flavour?
4. Not sure about the Bobek anyway - suggestions for the copper hop?
5. How much water will remain in the grains after draining ie how much extra water
do I need for the mash, to be able to drain off the brew length (+ a bit for evaporation)?
6. This will be only my 2nd or 3rd AG, so any comments gratefully received.

Thanks. When I brew this I'll try & post some pics on Brewday.

Update: Weds 22/4
I put the recipe thru Beer Engine at 70% efficiency (the appln itself doesn't display correctly for me, but the results are ok in the browser window) and it came up with this (had to make a few assumptions) :-

xmas70.JPG (73.42 KiB) Viewed 1002 times

hope I can hit that EBU figure.
At 80% efficiency the OG was 1.083, FG 1.015, Alcohol 9.1% ABV

[OldAl]

I must admit that I was hoping for a few replies to my query
Wanted to brew it this weekend, looks like I'll have to go it alone with what I've got.
Anyone out there please?

[Whorst]

I'd be concerned that this recipe will yield a very thin, dry beer. If I was brewing this beer, I'd ditch the rice and 1 pound of sugar. You're setting yourself up for a beer that's going to be dry as the Sierra Desert. Mash higher and ditch the sugar and rice. Just my 2 pence.

[OldAl]

Thanks for your reply Whorst, all comments are gratefully received.
You're right to suggest upping the mash temp.
I thought (incorrectlly) that a thin mash would produce more dextrins & a thick mash more maltose, but its the other way round. I think a mash temp of 67C (152-153F) is about right.

However if I ditch the rice & sugar, I'm going to end up with a strong bitter - SG 1057, FG 1013, Alcohol 5.7% ABV, colour 18 EBC (according to Beer Engine).
I was after a strong Christmas ale, pale colour, not too sweet, with an hint of orange.
The rice & sugar is to counteract the malt sweetness of a high gravity wort.
Maybe I could reduce the rice to 1lb (450 gm) and add 6oz (170 gm) of a low colour malt such as (???).

Please keep the replies coming, I can always brew something else this weekend.