First depot

Wasn't it borrowed stock to start with. But otherwise I suggest Edgware Road when it got its own trains?

I think the answer is with difficulty - and I suspect carriages were parked all over the system, wherever a siding could be squeezed in.
But the Met's own engine sheds and carriage shop were originally at Edgware Road, squeezed in on both sides of the line East of Upper Lisson Street (the - then - two platform station was to the west), with access in part by a 'traversing table' - there is a 1:1056 1871 plan (amongst others) available at oldmaps.co.uk - enter co-ordinates of 527232 181712 . They were where the space for the Edgware Rd rebuild of the 1920s came from!

I Beleive they used to sneal GNR locos in at night down the tunnels from kings cross for trial runs as relations with the GWR fell apart.

Anyone any idea where on the system there were sidings for stock?

Also does anyone know if they turned locos at the termini, or ran bunker first in the other direction?

Bunker first was the preferred direction because the smoke was behind them.

Dont you mean Mansion House?

I wonder what the original layout was like there, and at Paddington and Farringdon

Engines were turned to equalise wheel wear, rather than for running purposes, although that would be after the inner circle was finally completed.

Now this is just a thought, and I stand to be corrected by people who know their stuff, but as the 4-4-0 Beyer Peacock tank locos had bogies at the front, surely that would be the preferred direction of travel, as the bogies help to guide the loco around curves. Running bunker first would not, although it would be perfectly safe given that the correct, but perhaps reduced, speed would be observed.

I wonder if they used the triangles at Aldgate and Kensington to turn locos. Probably with the intensive service there wouldn't be enough paths to do it a lot.

Initially GNPBR trains were stabled at Lillie Bridge District Rly Depot.

Lillie Bridge stabled Picc Line trains from its opening until March 1933. Working Timetable (WTT) 125 of 13/3/33 was the first not to have Picc trains stabling at Lillie Bridge.

Incidentally, a handful of District Railway B Stock trains were also based there when they provided the service between Willesden and Earl's Court in 1914 and until the LNWR got its own stock.

Other incidentals saw Picc Line Gate Stock trains go to Ealing Common for heavy repair and the like in the early days, and some Picc cars were known to be stabled/stored in the disused car shed at South Harrow but only until c.1910 (no exact dates - sorry!).