The short answer
In temperament, a Clydesdale may be the kindest first horse in the world; in every other respect, he is the largest decision a beginner can make. These are the famous gentle giants, calm, patient and disinclined to drama, and a trained adult Clydesdale forgives novice mistakes with unusual grace. But a beginner is not only buying a temperament. You are buying sixteen to eighteen hands and the better part of a ton of horse, and everything about keeping him, tack, housing, transport, hoof care, is scaled accordingly.
The gentle giant reputation is earned
Clydesdales were bred to work in public: hauling carts through busy streets, standing at markets, ploughing in teams where a spook could wreck a day's work and injure the people around them. Steady nerves were selected for as rigorously as strength. The modern breed kept that outlook, and most Clydesdales meet novelty with a look rather than a leap, tolerate clumsy handling, and settle into a routine with real contentment. For a nervous beginner, that unhurried confidence is genuinely steadying; the horse's calm becomes the rider's calm.
Where size bites
Start with the ground. You cannot out-muscle a Clydesdale, so his basic manners, leading politely, standing for grooming, picking up dinner-plate feet on request, are not refinements but necessities, and a beginner must learn confident, correct handling from day one. Mounting needs a tall block or a helper, because there is no springing up onto a seventeen-hand back. Saddles, bridles, rugs and headcollars come in draft sizes, stalls and trailers need extra height and length, and your farrier must be willing and equipped to trim very large feet, which not all are. Feed and hay come by the tonne rather than the bag. None of it is a problem if planned; all of it is a shock if discovered afterwards.
The trained adult requirement
Everything above assumes the horse is educated. A young Clydesdale is still growing into his enormous frame for years, is clumsy in the way of all youngsters, and may not yet know his own strength; that is a horse for an experienced producer, not a novice. The beginner's Clydesdale is the adult who has been ridden and driven, has stood at shows and on yards, and whose reactions to traffic, dogs and machinery are known. Pay for that education gladly, because with a horse this size you are buying certainty above all else.
Try before you buy
Handle any candidate thoroughly on the ground yourself: lead him, tie him, groom him, pick up all four feet, and watch him loaded and travelled. Ride him with your instructor present, and spend time in the yard imagining your daily routine at his scale. When you find the steady adult who fits your facilities, get his shoeing cycle, feeding amounts and history in writing at the sale. KinsLe's Transferrable Profiles moves that profile, his records and routines included, straight to you, so the giant arrives with his instruction manual attached.