Percy Woodland.
G. Stevens won the Grand National five times, in 1856, 1863, 1864, 1869 and 1870, and won the Kentucky Derby three times, in 1988, 1995 and 1997. Of course, it isn't the same G. Stevens; the Grand National winner was George Stevens and the Kentucky Derby winner was Gary Stevens. But it's probably the closest to an answer you can get, since no jockey has won both races.
Liam Treadwell
Don't Push It (Jockey AP McCoy)
Red Marauder won the 2001 Grand National. Trained by Norman Mason and ridden by Richard Guest.
Twice
The 2008 Grand National was won by the horse Comply or Die, ridden by jockey Timmy Murphy.
The jockey fell off at fence 14.
He hasn't. Detori is a flat jockey and doesn't do the jumps.
The Derby for flat racing or the Grand National for jumps racing (National Hunt) Ascot Gold Cup.
Surely the grand national - jumps (4M 4F) Possibly the ascot stakes - flat (2M 6F) The longest flat race under Jockey Club Rules is The Newmarket Town plate at 3M 6F. The Grand National is run under National Hunt Rules.
The weights due to be carried by Grand National runners range from a minimum of 10 stone (140lb) to a maximum of 11 stone 10 pounds (164 lbs). This includes the weight of the "tack" (saddle etc) as well as the jockey.
There are many potential answers to that, and opinions would differ. The biggest jump race is probably the Aintree Grand National, held on the first Saturday of April near Liverpool in England. The Epsom Derby, also in England, could be argued to be the biggest flat race, though there are other contenders.