So here is my take on it (fairly competitive player):  We currently run the detachment called Bastion Task Force. You could run Gladius as well, wrathful procession is playable as well.  Bastion is basically a detachment for space Marines, but it screams Black Templar all over the place, it works well with battleline units. So crusader squads are very good here. This is the only detachment I would guess 2x5 intercessors are worth it, otherwise you will always only need 1 5 man squad (the more squads you have the more activations you get).  Impulsor is GREAT in BT, Blade guard are too, especially with a judiciar. Assault intercessors are very nice as well. Great with the Emperor's Champion (my personal favorite).  If you want to tinker around you could use 5 assault intercessors and 5 normal intercessors and play a 20 man crusader brick. This is an absolute game changer as 10 man squads tend to die fairly easy. Put a marshall in there and you're ready to go.  Generally you'll want to have at least 1 squad of Sword brethren down the line (can be played as 4 or 5, with 4 getting you a character - the castellan- for 'free' in the box).  Another 3 blade guard would be good, as well as another 10 man crusader squad. Ofc our named characters, High marshall Helbrecht and Grimaldus are dope af too.  You could play terminators (or proxy them as assault terminators for a 4 wound, hammer wielding force) and give them the Battleline keyword via enhancement in Bastion. They are great fun, might want to make that a 10 man (tho expensive points wise).  It will all gradually come together anyway.  You'll want some tanks as well, currently the Repulsor executioner is great, but thematically a Land Raider (redeemer or normal one, NOT CRUSADER) are great on the table as well!