mikepliek's page

Technicly you can use a shield with a illuminating shield boss so you dont have to hold a lantern in one hand, you can still hold onto your shield and keep going, though i believe its slightly weaker then holding an actual lantern
https://www.d20pfsrd.com/equipment/armor/shield-boss/

Summoning a creature isn't a "bonus", so pg 266 doesn't apply. You can absolutely use it multiple times to have more than one creature summoned.

However, you may be overlooking a couple of things that throw a wrench in the summon-a-horde plan. First, gravitic calling is a zenith revelation, so you can only use it every three rounds or so (depending on things like whether you have disproportionate revelations, for example). Zenith revelations require you to be fully attuned, and after you use them they drop you to unattuned. Second, you need to be facing a 'significant enemy' in order to build and maintain attunement to graviton. This means that you need to be in a particularly long combat to be able to get multiple summons off.

You would have three seperate instances of summon monster

round 1 Atune
Round 2 Attune 2
round 3 BOOM summon Critter 1

Round 4
Round 5
Round 6 Boom Summon critter 2 critter 1 has 6 rounds left

Round 7
Round 8
Round 9 Summon critter 3, critter 1s duration expires and goes back.

actually, you can go even further beyond that by taking the Perastria training feat at lvl 9, put 5 points into mysticism and boom. you can go something like this

turn 1: 1 point into gravition, use feat, spend 1 resolve point, summon, become unnatuned.

turn 2: 1 point into graviton, into gravition, use feat, spend 1 resolve point, summon, become unnatuned.

turn 3: etc...

aslong ofcourse if you willing to use resolve points you can keep summoning every turn