I'll start with the BP 70L. Whatever is growing well in there now, I'd keep. If you want something to fill the back then I'd go with Ambulia but seeing as you hate it maybe go with polysperma, I assume you know how to trim the plants and replant the cuttings? Then polysperma transitioning from the back to the mid ground with glosso in the foreground. I'd cover that wood in moss and tilt it so it goes from the centre front to one of the back corners.
The 31L, 2x 39w of T5HO lighting on such a small tank is going to be insane, even if you do run CO2 and ferts on it. Also, aren't 39W T5HO tubes 3ft long?! I'm hoping you made an error here or else there's a big issue. The hardscape in this tank lends itself to an iwagumi scape at the moment, I feel that adding too many plants and driftwood would ruin that but it seems you've got another look in mind. That front rock will take away from planting space and get lost so you'd may as well take it out. You need to think about what it'll look like when it's all grown in, a forest would hide that rear rock so a change of hardscape seems to be in order here. You could always make that sword your focal point, hairgrass in front of it and stems behind.
No idea what that mystery plant is sorry.