Well it depends. What size tree do you want and what size trunk do you want your bonsai to have. A zelkova (or any other tree) grown aggressively in the ground or in a box has some advantages. Thickening and growth happens much faster. Then you can start your refining process in a pot. But there is nothing wrong with slowly developing a tree exclusively in a pot. It has its beauty and merits, it just will take you that much longer to get there.
Initially I approach all my trees using a combination of wire and directional pruning. As the tree develops I then start to rely less on wiring and lean more into directional pruning. Wire scars on smooth barked trees are a problem and often you will need to cut off the branch and start over if the damage is significant enough. So when you wire, you must be VERY vigilant!!