Laceleaf maple, large pot?

[Fluke365]

I bought this dwarf laceleaf maple, velvet viking is what it said in the label. My plan with the tree is to have it in a larger pot until I get my new home in a few years. I want to plant it in my yard on a bouldering landscape as a centerpiece of my bonsai garden. I would like to make it a nice little bonsai but the graft scar is a little hard on the eyes...so my questions are followed...
1. What's size pot would be recommended
2. I usually use akadama pumice and lava rock mixture on my trees but this would be spendy in a large pot, what can I use thats cheaper?
3. Being that it's going in a larger pot eould I need to do any root pruning or could I slip pot it? Bit of a noob here and I don't want to hurt the tree as it wasn't cheap and I've found out the hard way is very weak in the crotches of the branch

 

[Srt8madness]

Potting soil works fine for trees. I would wait until spring to mess with repotting.

Pot size, not much bigger than what it's in, assuming it's filled out current pot.

 

[Scorpius]

Root work in early spring just as buds begin to show color and swell.

 

[Shibui]

Trying to work out what pot goes in a boulder landscape but now understand the pot is temporary until you get the boulder landscape to plant this in the ground.
Generally 1 or 2 sizes up when changing pots but it could probably manage in the current pot for another year. A possible drawback of the same pot is if it is already getting pot bound it gets harder and harder to water well. Going too big will only cause problems with water retention and when you need to plant it out you'll need a much larger hole.
Slip potting at any time is OK. Just tease out some of the outer roots when up potting so the roots will spread into the new soil but leave the root ball largely intact and backfill the larger pot with fresh soil. You should not need much extra soil to up pot a tree this size.
Potting soil is fine in larger, deeper pots. Mostly causes difficulties in shallow pots which is why we use more open, inorganic soils in smaller bonsai pots.
All Japanese maples have brittle branches so take some care when handling but remember that it will always grow back so a few minor breaks is not the end of the world.

 

[Fluke365]

Thank you for the suggestions, and when I get my forever home I plan on planting this in the ground with a boulder landscape around it. So eventually will be in the ground. It is already getting rootbound in its current container, so I feel a slip pot is needed...