On your first question the major problem was not necessarily speed, which did improve a bit for example the French Renault FT could make a bit over 4mph, but instead endurance. They were never able to solve the range and reliability problem given the technology at the time. This meant that even light tanks like the FT only had an operational range of about 40 miles. Breakdown rates were also incredibly high, and during the final offensives of the war in 1918 the British rapidly ran into a situation where they had to deemphasize the use of tanks simply because they did not have enough that were running.
Suggested readings: (this is a mix of books and articles)
* The Infantry Cannot Do with a Gun Less: The Place of the Artillery in the BEF, 1914-1918 by William Sanders Marble
* The Dynamics of Doctrine: The Changes in German Tactical Doctrine During the First World War by Timothy T. Lupfer
* The Marne and After: A Reappraisal of French Strategy in the First World War by Douglas Porch
* The Evolution of British Strategy and Tactics on the Western Front in 1918: GHQ, Manpower, and Technology by Tim Travers
* Operational Art and the German Command System in World War I by Bradley John Meyer
* Not Glamorous, But Effective: The Canadian Corps and the Set-Piece Attack, 1917-1918 by Ian M. Brown
WOW, thank you! I honestly didn't expect more than a snarky link to Wikipedia or something. Do you have a favourite charity? I'd like to say thanks by donating a few bucks to them, if that's OK with you?
Suggested readings: (this is a mix of books and articles)
* The Infantry Cannot Do with a Gun Less: The Place of the Artillery in the BEF, 1914-1918 by William Sanders Marble
* The Dynamics of Doctrine: The Changes in German Tactical Doctrine During the First World War by Timothy T. Lupfer
* The Marne and After: A Reappraisal of French Strategy in the First World War by Douglas Porch
* The Evolution of British Strategy and Tactics on the Western Front in 1918: GHQ, Manpower, and Technology by Tim Travers
* Operational Art and the German Command System in World War I by Bradley John Meyer
* Not Glamorous, But Effective: The Canadian Corps and the Set-Piece Attack, 1917-1918 by Ian M. Brown