OP, think about what "portable" means to you. Ex: move it across the room, from one end of the house to the other, inside to outside, up or down stairs, down the driveway to the car, etc. Then look a that route. Smooth floor. Thin carpet, thick carpet, door sills, curbs, step down, etc. This will tell you a lot about what you need. Those small caster things are neat but cannot do stairs. The Stanley or Husky hand truck type things will handle irregular floors and journeys much better. Ex: up the stairs and out onto the back porch. The larger the wheels the better. You could even figure out how to lash that table to the thing. Maybe choose a design that will hold your current tools and many of the others you'll get. And, maybe some consumables ( grease and lubricants and solvents and paper towels, etc) but not all your parts. Or, maybe just the parts for the current build. Seriously manage the weight n potential weight.

Figure out what you want and HOW you're going to use it. Then buy just a bit more than you'll need. You'll grow into it.

I have an old three compartment Craftsman box I bought from our hay guy for $5.00. Cleaned it up and it holds all the bike tools I regularly use. Several others are seldom used (DO alignment tool, heavy duty chain whip, frame alignment tool) so are stashed elsewhere. Not readily to hand.