For sidearms choose between Valiance and either Pulsar to start for guns. A sword sidearm depends on how you use swords. When I was shifting from swords to bombs my main sword was GFaust and I obsessively used its basic combo. Not by spamming the basic swings around, I learned how to time it and everything. Nets a lot of knockback and if its second swing curses the group of enemies you hit you can bomb to deal damage while they hurt themselves. I heard you like dealing damage to multiple enemies so we took a status that deals damage when the enemy attacks and let you choose to use other weapons that inflict statuses and/or deal raw damage at the same time. With gun sidearms it depends on whether you want knockback from close or far range since both can get turrets. If you try to face T2 and T3 turrets without enough experience in evasion Pulsars are easier but eventually you get to the point where you can use Vaporizers to fight turrets and not give a shi-

For your bombs it also comes down to preference and filling desired roles. Agni and Nitronome both fill neutral damage but both have a disadvantage: Nitronome has an obnoxious animation which can annoy allies and Agni is useless against fire resistant enemies. If you absolutely have to get a shard bomb I recommend going for one of the two original lines, Scintillating Sun or Shocking Salt. Both have a decent rate to inflict a status (stun and shock, respectively) and a big family bonus. The only downside compared to their statusless and family-bonus-less branches is a tiny sliver of damage. The element shard bomb is useful if you need to deal that damage type but that will not always be the case. Definitely get the Snarbolax bomb for pierce damage. Other than that what you get is up to you. Vaporizers help your team by inflicting statuses to a wide area, Graviton/Electron have a suction effect which pulls enemies in so your allies can beat the liquids out of them, Blast lines can either be obnoxious or helpful in knockback depending on the situation, and the Seerus bombs only available through the expansion are pretty gudd for shadow damage.

If you want something simple and practical for early bombing aim for Volcanic. It has fire resistance and gives +2 bomb charge per part at 5*. If you plan on stuffing a bunch of charge UVs in your pants for your bombs you can get Bombastic for +2 bomb damage and freeze resistance instead but as a new bomber you probably lack the green to be call Punch mean. If you know what I mean. Mad Bomber is more for bombers who can handle the status weaknesses but receive +2 bomb charge and +2 bomb damage per part. The normal defense on it is lower than the other three lines but you get double the bomb bonuses. The explosiveness has been doubled. Lastly we have Mercurial Demo which is only craftable at the end of the Shadow Lair. It gives +1 movement speed and +1 bomb damage per part, meaning it sits in the same boat as Bombastic: you have to get bomb charge somewhere else. If you can afford trinkets they exist for all weapons. You can get H10 on your bombs for +2 charge then get the remaining +4 by crafting two of these but you have to pay the constant trinket slot fee (150E a month to buy each upgrade yourself, ~6kCr to buy from other players). If you want something inexpensive and simple go for Volcanic but otherwise there are other options out there. Somewhere. Over the rainbow.

If you want basic equipment tutorials check here and read aboot stuff. Also check this place for even more stuff.

Acheron and the other Brandishes are not sidearm swords. They are primary offense weapons. A sidearm is something you switch to occasionally for a few seconds at a time to make the battle more comfortable for you. Like a pillow. I wish I could use a pillow as a sidearm. Smother enemies with it. Its softness is deadly.