Hi,
The number of hotels available is considerable, but your visit is planned during a peak visiting time, so I'd recommend getting it finalised as soon as possible. For booking engines - I'd recommend Laterooms.com or Booking.com, for having a good pool of hotels and being large enough to offer good discounts.
In terms of travel - I'd recommend travel cards, over Oyster. The best bang for buck is either the weekly or the 3-day, 2-zone Travelcard. (your hotel room should ideally be within zone 1-2).
The website I run covers the ins and outs of transport and also gives a guide to the best sights and attractions. If you have any further questions - direct them either here or at the site and I'll point you in the right direction.
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