Divine Robot grants arsenal access the same way Real Robot does (only with half capacity) so Divine Pilot 8 gives you Arsenal III and, if you go with an Alteisen or a WeissWritter, 62.5 arsenal space.
If you don't have any other plans for it, I would recomend the Fission System for Reactor II, and possibly the Hybrid Armor for an armor, DR, and Fort save boost.
That leaves 12 space which is enough for Ablative Plates for 9 extra HP and a Cartridge because it only costs 2 space. Which reminds me, I need to put ablative plates on Aden's mecha.