TL;DR on the bottom
I use three weapons. Its honestly not harder than switching between 2. Especially if you scroll for weapon switch. Going up or down gets you a different weapon. And if you really have problem switching, just kite around them while you slowly look at what you are wielding. This seems to be an attempt at an all around set for every single gate at once. Why not build multiple sets? One piercing set, one shadow set, and one elemental set.
Your weapons: Sudaruska is a nice weapon, but you have some information wrong. The sealed lines can also perform the hit, hold, and let go for a 2nd hit further away. In fact, i believe all the other weapons can do this transition from first to second hit. The charge attack leaves you plenty open to something kicking your butt, especially as this is a solo situation. Seeing your fascination for knockbacks, why not a leviathon? Plenty knockback, aoe hit, and a faster recovery with the charge, not to mention in its regular combo. Sudaruska does not do more damage than sealed lines. I can hit 5 with my avenger, and have the charge carry some even further for more damage. Granted, the initial hit is very powerful, at the cost of slow movement and not hitting while charging.
The gun: As I do not use guns with knockbacks, i'm not sure. But from what i see, you can interrupt enemies even if the damage is resisted. Again, don't take my word for it. Does not the iron slug have the same stop>shoot as the calla?
Armour: Generally, armour is used for the bonuses it gives. And status resistance. Your shield should be taking the hits, or it should be dodged. And you should have different sets for different enemies. Not necessarily an entire set, but mixed pieces work well if you don't have the funds to craft them all.
Shield: I'm a huge stickler for shields. Get the right shield for the right monsters. You really should have multiples of this. A piercing, elemental, and shadow. I've regretted the times when I took my owlite into a RJP run. Not a huge amount, but still. Again, like the armour, dodging is more important than taking the hit. A broken shield is not fun to use. Most shields of the appropriate star has enough bump to get you out of tight spots. But the omega shell does look badass when its not being held.
Bomb: Well.... okay. Here's the thing. Bombs in SK doesn't exactly work like RL bombs. They aren't for dealing huge amounts of damage, or you wouldn't see the wolvers running around everywhere in Haven. Bar the nitronome, most bombs used are for status effects.
Like Bopp said, it is easy to sustain slots. They last for a long time, 30 days. 2 weapon slots at 250 each, and 2 trinkets at 150 each, amounts to 800energy. Assuming all ce, and assuming high ce prices at 7000/100ce, thats 56000 crowns. In a month. Each RJP, not counting previous floors, nets about 4k? Might not be right, but ballpark figure. 14, say 15 for good measure, trips. One run a day, or even one run every 2 days on mist. And you have enough crowns. Trinkets arent even necessary to solo well. So its entirely feasible to sustain 2 extra slots. Most people make do with 1 extra slot, covering all three damage bases.
Alright, say you really don't want to spend the time getting crowns for slots, then having to spend time to switch weapons. 2 weapons. One piercing, one elemental gun. Fiends and beasts fall like flies. Puppies don't last long, even behind bottomless pits. Constructs will never get close enough to touch you, same with undeads. What I'm trying to say here is, with 2 specialized weapons, you do effective damage to 4 types of monsters, and neutral/base damage to 2 others. As compared to having 2 normal weapons, which does neutral/base damage to all families. Mix and match weapon types to fit the stratum you are descending into. Check the gate map from the gear on the top left to see what kind of monsters you would be facing.
Tl;dr: Don't be afraid to branch out. Try out specialized equipments. Know the priority, depending on the gate. Do you run multiple different gates to have variety? Or do you farm RFP/FSC for crowns? Having a good weapon, a semi decent shield, and a armour that vaguely matches the monsters you plan to fight is almost necessary.
My setup is for both solo and group: Avenger, faust, and volt driver. Since i mainly run RJP, i use the ash tail set and a twisted targe. Piercing for jellies, dodge the lumber. Faust for the jellies, avenger when its me and lumber 1v1. Charging that volt driver into puppies/lumber+jellies makes me happy.
Disregard everything i said if you just like the looks of your equipment.
Even if you are free-to-play (F2P), it is not difficult to maintain a cash flow that lets you use three weapon slots. Farm Strata 4 and 6, particularly arenas, RJP, and FSC. And switching among three weapons takes, what, 0.1 seconds longer than switching between two weapons?
Even if you have only two weapon slots, it is advisable that you carry two non-normal damage types. For example, a piercing sword and elemental gun. Or a shadow sword and elemental gun. Or two swords.
Also, many F2P players play in groups. There is no particular reason for a poor player to play solo.
I'm not trying to disparage your set. I'm just arguing that being poor doesn't make any sense as its justification. Its justification is that you like it. :)