The IGN & ACC have more than enough capacity - automotive 30A relays rarely consume more than 250mA.
ACC cuts off when cranking/starting whereas IGN doesn't.
Your dc-dc converter is probably ~2.5A input. At your battery I assume a 5A (or larger) fuse supplying a 5A or fatter +12V cable to your relay contacts (+12V to 30; 87 to dc-dc converter's +12V input.
You could use a 1N4004 etc diode in EACH input's +12V to common for actuation - eg, IGN, ACC, manual +12V, low-voltage device, could all control the same instead of a relay for each. Any 1N400x diodes will do, eg, IN4001 upwards, but 1N4004 else 1N4007 tend to be the commonest.