He sounds like a very fortunate child! You are doing all the right things to keep him happy, well adjusted and intelligent.
Is Dad around? Are there any NCT groups, Surestart, or other baby/toddler activities in your rural area? If not, would you be in a position to consider running one, even if on a very small scale, or if only fortnightly?
That is brilliant he sees the ponies! Try to involve him with them for a long a time as you can spare. Our DS used to love to watch a tiny stream that ran through our village, and as neither of us were working at the time, he could watch it for as long as he wanted to.
Contrary to what many people might think, babies DO NOT need constant activity and stimulation, but periods of comparative quiet, relaxation and gentle bonding with a parent. Everything is still totally new for him, as he hasn't been out of the womb for very long, and he is still trying to make sense of the world.
Soft toys, a comforting blanket, and a bit later on Duplo bricks and animals (a farm set might be appropriate!) will probably be his favourite toys. Read to him as much as you can, maybe cloth-books that he can play with. A set of Beatrix Potter books may be enjoyed for years; when he is old enough perhaps he can visit the Lake District and see the real locations, many of which still exactly match the book illustrations.
You won't believe how quickly time will go by, and if you can, keep a journal or scrap book of his progress, which you can share with him in ten or twenty years' time! I (Dad) was learning to play the electronic organ when DS was born, and at a few months old he was 'playing' on it too. At two years, down on the floor, he pressed the bass pedals to go with my chords, and at four or five years he was playing his own tunes.
Regarding 'Baby Books', I think Penelope Leach is still one of the best; there may be more 'modern' books, but tiny babies don't need to be modern! This link tells you about her, and "Your Baby and Child" is her major book. Amazon is NOT always the cheapest place for books, and I often find The Book Depository cheaper for some titles, so shop around.
Come back if you have any specific queries, but it sounds like you are right on track!