sounds like a polyembryonic seed. only one of the branches will be true manilla and will be dominant and the others should be chopped or may eventuslly die. keeping these will take energy away from the main actually and will make the desired trunk less cold hardy.

manilla and asian varieties are generally less cold hardy than monoembryonic (ie: not true from seed) indian varieties like neelum

Are you sure it takes away energy? if all the suckers are cut,then instead of 20 leaves,it might only have 6-or less. I havent heard of a multi trunked mango,but this is an extreme climate for them,so maybe,MAYBE,an extremely different approach is needed.
The gold nugget will be grown conventional.

its not a multi trunked variety, all mangos are single trunk trees.

the seed variety is polyembryonic. if you choose not to prune the weaker shoots they will die off at a later stage.

its good that it is polyembryonic because it will come true to the variety of the fruit it came from versus a monoembryonic seed. when a monoembryonic mango tree is grown it is not the same variety but a 'seedling' of that variety ie: Graham is a seedling of Julie.

where are you growing this tree? if you get frosts however slight it will need to be protected during the winter with fabric and or christmas lights.

the link below shows pictures of a jackfruit seedling that is also polyembryonic

Here is a link that might be useful: polyembryonic jackfruit seedling

Its growing in the east San Francisco bay area. Some years no colder than mid 30's,other years we push 32 or lower in a really bad year-like 07.It cut the tree from 9' down to ground level,then last summer it grew to be 3'..then cut to ground again this winter.Right now its a bushy 1'. I think I will let it sort out its own leader,maybe when one is the clear winner I can prune off the others.
This winter it gets covered for Dec-Jan our only frosty months.