New to Bonsai and am asking for advice on my first tree.

[Jplane]

Hello,

I have been gardening for some time on my appartment balcony and am excited to get into Bonsai! I have read a beginners book and watched many videos. To begin I purchased a decent looking Boxwood at the nearby garden center (see attached). I was drawn to the interesting nebari and the two trunks.

I am planning on pruning and wiring while the tree is still in the nursery pot. I have done a sketch where I have tried to draw the tree as is after planned cuts (minus foliage because I'm not good at drawing it), then I erased and redrew branches to simulate wiring into new positions. I am looking for advice and feedback on my design before I go for the pruning and wiring. Additionally, I've seen that criss crossing roots are poor and should be removed (removing one marked) , but I'm curious if there's any other work I can do on the roots to enhance their appearance. Also, while leaving this tree in its nursery pot, should I add more soil to cover some of the roots?

 

[Shibui]

Was going to suggest consider tilting the tree to make the major trunk more upright but had a look at your drawing and discovered you have already anticipated that.
I suspect you are trying to retain all current branches in the new design. Most beginners do this. Bonsai is often about saying more with less. Several branches growing close together on a trunk will almost certainly cause the trunk to thicken at that point leading to what we know as inverse taper which spoils the flow up the trunk(s). Consider removing some close together branches. This will alleviate the swelling problem and leave room for the remaining branches to produce side shoots and become real branches rather than sticks with a few leaves.

Also look for places where branches grow toward the other trunk. Normally, lack of light stops these branches growing while those growing out and away get bigger and stronger. Left branch on smaller trunk and right side branch on larger trunk for example.

Thick branches in upper canopy can cause problems with perception of distance/height. Normally we see distant objects as smaller than close objects. A bonsai with thicker low branches and thin upper branches fools our mind into seeing a much larger tree.
Ditto with trunk taper. Thick down low tapering to thin up top gives the impression of older, larger tree.

Long straight branches are a feature of young plants. Older trees have well ramified branches with lots of secondary and tertiary branching. Tapering branches also look older. Drawings appear to indicate you plan to retain full length of the current branches which are almost all straight, lack taper and ramification.
Just trimming the tips will see any new shoots grow from near the ends. Pruning the existing branches much shorter will appear to be a setback but well worth that step backwards for the extra taper and ramification it should give you in the longer term.

I've seen that criss crossing roots are poor and should be removed (removing one marked) , but I'm curious if there's any other work I can do on the roots to enhance their appearance

Tilting the tree will help a lot as the currently exposed roots will be closer or under the new soil surface. You may also uncover some more roots on the opposite side to balance the dominant right side roots.
No problem removing a few roots any time of year. Root marked could be chopped or moved to follow the line of other roots. You may even consider removing the next highest root (immediately behind) as it will then be much higher than other roots but that will depend what you find after the trunk is tilted right.