I think everyone approaches projects differently. I would replace all the consumables (filters, oils, etc), get it running, and go from there.
I've seen too many projects where the person tears the project down to nuts and bolt, then runs out of time, money and interest. The project is then a pile of parts. It kinds of depends on your ability to keep at it. It's hard to stay motivated when you can't ride your pile of parts and the end looks way far away.
I agree with just seeing if the thing runs as a first order of business, and then go from there. As a precaution, let's say that you don't even look in the gas tank, you just throw a gallon into the tank, and use a temporary battery to attempt a jump-start. The engine turns-over, but the carbs start peeing gasoline everywhere, out the overflows, from the float bowls, both the drains, and the bowl gaskets. Bad news! I hope you're doing this outside and not within vapor-carrying distance (30 ft is possible) of a gas-powered hot water heater or a furnace. You need to stop, clean up the spills, and drain any gasoline remaining in the bike to prevent it leaking further. This is common-sense stuff, but impatience can ruin the best of intentions.
Using a temporary tank is a good way to bypass a gunked-up, rusty bike gas tank. Checking the gas lines for clamps properly placed and fastened, and rubber/plastic gas hose not leaking should be done. A quick screwdriver use can check for any residual fluid in the float bowls, but if it's been more than a few months' of inactivity, any gas has probably reverted to varnish and brown/black gummy residue. A year or more, and that's probably become hardened scum.
If I knew the bike had been inoperable for more than a few months, I'd probably just expect I have to remove the carbs, and do a thorough disassembly. I use an ultrasonic cleaner, and rarely do I need to do it a second time. Jet blocks out, brass jets inside removed, and compressed air after the soak to clear passages. If three carburetors' passages flow a similar amount, and one doesn't, you know what needs to be cleaned again.
A generic gas filter will fit in-place of the OEM, and is much cheaper. Turn on the fuel pump w/the hose into a receptacle and see what volume you get out of it. If it passes muster, use the accessory gas tank, hook up the gas, and having checked for spark, see what happens. You did change the oil & filter? Perhaps you're lucky and it starts w/o issues, but w/o the air filter, it's not going to run as it should, it needs to be clean and in-place, and then you can see about the engine accelerating smoothly.
This is some basic stuff, many people are likely to do similarly.
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