I think you have described my wife Amy's character, Boffin, in my Iron Gods campaign..
Boffin is a dwarf gunslinger with the gnome-exclusive Experimentalist archetype, the Technologist feat, and the Local Ties and Skymetal Smith traits. She was born in the town of Torch and has worked in odd smithing jobs since she was old enough to swing a hammer. I let her combine the skymetal item from Skymetal Smith with the experimental firearm from her archetype. Whenever the party found technology, a workshop, or a computer system, she read the manual, i.e., maxed out Knowledge(Engineering) and Disable Device, learned Craft Technological Item and Craft Technological Arms and Armor. And she collected an e-pick, veemod goggles, an autograpnel, a trauma pack plus, and wirejack cybernetics. At 7th level, after Boffin refurbished the broken wreck of a shuttle spaceship, she needed a pilot. However, Boffin was an introvert and did not want a normal employee. So I gave her a robotic cohort, repair drone and pilot Dwalin, for her Leadership feat.
The key for Boffin was to start with a gadgeteer theme and introduce more technology as she went along. No class starts with technology, though some of the archetypes boost technology use at 4th or 5th level.
The technology-themed archetypes in the Technology Guide are Cyber-Soldier (Fighter Archetype) which starts at 5th level, Iron Priest (Cleric Archetype) which heals constructs, Technic Scavenger (Rogue Archetype) which uses glitchy technology better at 4th level, Savage Technologist (Barbarian Archetype) which can use firearms, and Techslinger (Gunslinger Archetype) which can use technological firearms but starts with a gunpowder firearm like other gunslingers. The Technology Guide offers the Technomancer prestige class, which sorcerers, wizards, witches, and arcanists can start as early as 7th level.
The Galvanic Saboteur (Ranger archetype) and Numerian Liberator (Barbarian archetype) from Pathfinder Player Companion: People of the River hate technology, but the Galvanic Saboteur does have a Reprogram ability that works like wild empathy on constructs.
Another archetype that fits well with technology is the dwarf-exclusive Forgemaster (Cleric Archetype) from the Advanced Race Guide. Boffin's robotic cohort Dwalin leveled up as a cleric of Brigh with the Forgemaster archetype.
Next, let's cover the annoying details. All the high tech in the Technology Guide except cybernetics has either a limited number of uses or consumes charges. If your character cannot restock the depleted items or buy batteries, the tech will become useless. A battery costs 100 gp for 10 charges. A hundred charges in ten batteries should last through a module, so your character could spent 1,000 gp to stock up on batteries. Generators that can recharge items without batteries are considered priceless. The spell Recharge can recharge an item without batteries, but the diamond material component costs more than batteries. A Techslinger can spend grit instead of charges, but grit pools are small.
Cybernetics is the exception, but it is too expensive: a cybernetic eye or ear costs 4,000 gp for a +2 to Perception, dermal plating costs 4,000 gp for +1 natural armor (twice the price of an Amulet of Natural Armor), cyberfiber muscles cost 8,000 gp for +2 to Strength (twice the price of a Belt of Giant Strength), etc. And except for implanted weaponry (10,000 gp plus the price of the weapon) they merely boost the character's existing abilities.
For high-tech weaponry, Boffin favors the autograpnel. It shoots a spiked adamantine grappling dart with a cable attached, one charge per shot. Boffin shoots it once, and keeps the line taut to give grappled penalties to the target while the melee party members engage the target in combat. Due to the gunslinger's Nimble ability, Boffin has the highest AC in the party, so she does not mind if the grappled creature rushes her. If she wants to do damage more than once, she hands the autograpnel to another party member to maintain the grapple and shoots with her blunderbus. The autograpnel is one of the cheapest technological weapons at only 4,000 gp.
The stun gun is another option affordable by 5th-level wealth, at only 3,000 gp. The chainsaw is the cheapest at 2,700 gp, but it does not feel high tech. The stun baton is only 5,000 gp and packs a hefty wallop for a light weapon.
On the other hand, a laser pistol costs 10.000 gp, almost your 5th-level character's entire budget. That cost can be halved by buying a timeworn laser pistol, but timeworn weapons can glitch and cannot be recharged, so you would have to definitely go Techslinger to use one.
As for a robot companion, there are no rules for it. Perhaps your GM would agree to substitute a low-CR robot like a repair drone, observer robot, or arachnid robot for an animal companion. Robots do not require charges; however, they are not healed by Cure spells nor channeled energy, so they won't serve on the front line as well as an animal companion.
I am curious about the details of point 4, "It has to rely on technology instead of magic." Does that mean merely that your character would replace standard magic items with tech items, such as dermal plating for natural armor rather than an Amulet of Natural Armor? Or that you don't want to play a spellcaster? Or that your character ought to be entirely free of magic, not even a +1 sword? The spell Make Whole on the cleric and sorcerer/wizard lists is an excellent way to keep technological items and robots in repair.