TEI has very few extremely effective warships and whole fleet of Capella-era warships basically untouched. GTVA in Nostos is more balanced, having all older warships retrofitted but no truly superb warships like Erebus. Phobos is probably comparable to Bellerophon, but the latter has more sustained nature of dealing damage. Phaeton would be outmatched by Erebus [except shockjumping], but Boreas can easily rival the Titan.
I think BP-GTVA would succeed at offense against the EA, but would struggle if the EA is the agressor. Both TEI-GTVA and EA are extremely potent at hard-engaging isolated targets, but EA can do it only thanks to Lindos-class destroyers. If EA decide to blitzkrieg TEI fleets [even accepting considerable looses], they would gain the upper hand. TEI would not be able to respond quickly due to the numbers EA can muster to the battle.
From technical side, both fleets would require rebalancing. TEI ships in BP are balanced for "subspace chess"-style warfare, while missions in Nostos favours slower ways of dealing damage. Also both mods comes with dedicated sets of armor and damage types.
I'm not BP expert, but I would expect utilitarian approach from the Steele. The mind behind the EA invasion is Admiral Falon, who is potent tactician on his own. I guess Steele would hunt down important figures in EA fleets [like Admiral Spiros] to cripple coordination of storming EA fleet, then strike to hit the beast in the heart.