Does a tube amp's wattage needs to match or be close to the speaker or speaker's power handling ? Can a small amp push high wattage speakers or a large 4X12?
Speakers do not necessary need to be close in power handling to the amps output so long as the cab has greater power handling than the amps output power (wattage). Guitar amp speaker have sensitivity ratings of 95 db to 101 db. This means speaker with produce 95 to 101 db with just one watt of power a one meter of distance!
Remember wattage and volume is not a linear relationship. To be twice as loud an amp must have 10X the power. So a 5 Watt amp is half as loud as 50 Watt amp with all things equal (they rarely are though) . While a speaker can handle lots of wattage a small amp will be more than powerful enough to get that cone moving.
Whether or not you like the feel and sound of high wattage speakers or speakers rated well above an amp power output is another matter. Higher wattage speakers have less cone breakup and different distorting characteristics: typically have more lows and smoother highs. The speaker parts themselves often are stiffer and have more mass so high wattage speakers tends to be less touch sensitive. Some companies have spent lot of time addressing this issue and have speakers that react and play far more like their low wattage counterparts.
Putting a low wattage amp through a 4X12 can sound great!