There's no need for a massive assembly plant to produce a lot of drones from dual-purpose components. Most of these components arrive across the EU border and go to random warehouses that have been converted into assembly shops. There the drones are put together, flashed with the latest firmware and sent to the armed forces, where they are armed and launched.
The bigger problem Russia faces is the surprisingly sorry state of its AA. It's been designed to detect and intercept strategic bombers and multirole fighters, but it's been almost 40 years since Mathias Rust, and it still can't handle a cheap and slow flying target, relying only on point defense systems that can be and are overwhelmed. Ukraine has inherited the same Soviet tech but managed to build a better detection system that collects and processes the data from thousands of cheap listening stations across the country.
1. Putin thinks the disintegration of the USSR in 1991 was a historic disaster and wants to reassemble much of it as some sort of new "Russian Empire" in order to control more resources and establish defensive space to protect the motherland against a future foreign invasion. He sees Ukraine as a fake country.
2. Russian demographics are collapsing and Putin himself is aging so this was his last chance to take decisive action. Despite limited stockpiles of advanced weapons, waiting would have made an invasion even harder.
3. Putin has surrounded himself with loyal yes-men who curried favor by telling him what he wanted to hear instead of giving him accurate information about Ukrainian politics and military capabilities.
4. Putin perceived Joe Biden as being particularly weak and unlikely to take decisive action.
5. Russia's recent invasions of Georgia (2008) and Ukraine (2014) had gone fairly well so it wasn't irrational to expect a rapid victory.
To be clear I'm not trying to justify or excuse Putin's decision (I hope he loses) but rather to explain how he might have reached it.
Israel isn't going to sell advanced weapons to Russia in current circumstances. It would be impossible to hide. Intelligence analysts can pick apart little fragments from a missile explosion and determine where the components were made. It's not technology that Russia lacks but the capacity to manufacture that technology at scale with acceptable quality.
China is making a fortune selling weapons and dual-use equipment to both Russia and Ukraine. But they don't sell the good stuff because they don't want sensitive technology to fall into US hands, and because they want the option to bite off a chunk of Russian territory later.
The airport raid by SF on the first day of the war arguably came close to success.
Also Iran.
The "yes men" told Putin the military was able to do it. Probably they even thought it was, because everyone below them - right down to the individual soldiers selling off their fuel and ammunition - said everything was a-ok.
Even so, the initial invasion was a near-run thing.
40k Tons of bomb were dropped on Berlin in WW2. That's nearly all explosive payload too.
That's about equivalent to 80k modern cruise missile warheads.
The US has built less than 5000 Tomahawk missiles ever.
Russia has fired approximately 6000 missiles into Ukraine in the course of the war.
This is why the US still maintains a fleet of ancient "Bomb Truck" style bombers in the B52. Nothing compares to 100 B52s flying over a target for weeks. They allowed us to drop 20k tons of bombs on Vietnam and the surrounding countries. A horrific capability.
Gaza is a combination of Israel being utterly fucking insane and apparently desiring to terrorize people, and the fact that Gaza is super tiny.
But flattening cities is a WW2 strategy, and it didn't actually do much to win the war in the end, only cause unnecessary civilian suffering.