1. magnus, like TM, have dual wield skill, maxed at lv5, unlike Swordmaster / BT that have lv10
2. i might say sword, so u can use Sonic Boom
3. its all comes down on how prepared u are for lvling, if u have all the needs to reach 110% crit, then i say STR, but if not, DEX
4. magnus can be 1h sword + shield, that if pushed to its limit can have high dps and tank at same time
5. theres quite a lot of magnus build, u can try search in the forum and see if one fits u
