If you have little time for my blog articles right now, you can approach big two handed swords just consulting this list of common questions. Forgive me if some answers are somehow approximate, this page is not meant to be 100% exhaustive!
Short answer is: they are pretty much the same kind of sword and the name changes for Italians, Iberians and Germans. Shape and ratio differ slightly with regional differences and styles as well as with different decades, but old cross-language dictionaries tell us that these names referred to the same thing.
No, it isn’t. Until today no period source has been found that proves Zweihänder is a word coming from 16th century or earlier. It probably came in use during 19th century, even though no specific research to confirm it has been done yet.
No, they don’t. Most of them do not reach 3,0 kg and when they do, it is less than 4,0 kg. Heavier swords exist and they are greatswords as well, but they are usually considered parade or cerimonial swords due to their weight and unpractical dimension.
Longswords are those swords that requires both hands as well, but that weight less, do not exceed the armpit height and can be belt-fastened at the waist inside their sheath. To my knowledge, the name is a neologism (as well as bastard sword), while in medieval time they were known simply as spada (sword) or spada a due mani (two-handed sword), at least for Italians.
Check James Clark’s video on his Youtube channel Montante Niño. Unfortunately he is no longer in HEMA but, in my opinion, his videos are still the best material to look at. 16 Figueyredo’s simple rules give you enough to train A LOT.
Consult Wiktenauer! This is the list of almost all the greatsword treatises and sources we have. Do not forget that there is a longsword category too, even though it is not exactly the same thing.
I would suggest two options: Arte de esgrima (1599) by Domingo Luis Godinho and Memorial da prattica do montante (1651) by Diogo Gomes de Figueyredo. The latter is available on Wiktenauer, follow the link. Godinho is only available in his English translation inside the book Iberian Swordplay, absolutely worth buying.
Facebook is the right place so far. Make sure to enter the group Montante Swordsmanship! Uploading videos on Youtube or Instagram (with the right tags, like #iberianmontante or #spadone, for example) is another way to collect advice from other hemaists.
Right now, if we do not consider fencing-topic books, the absolutely best book so far about greatswords is Two Handed Sword: History, Design and Use by Neil Melville. However I am writing one myself.
Buy a stick as high as you from a bricolage store and train with it. I did so for almost one year, before to get mine. With a little more money and hand work you can craft something more sword-shaped, as I did: fix a curtains bar wood pommel to one end of your stick with a screw and add some tape to cover the right length of what you will grab as a handle. If you figure out how to, you can even add a crossguard. If you can spend 100 € and something more, you can consider a nylon waster.
It is a training sword made out of nylon. They are way less expensive than a steel one, they have quite a proper weight and they are a good choice. They wabble a bit and are not that good if you want to spar with them in same-weapon fighting (they do not behave like steel when the blades crosses or beat themselves). They are good for solo drills and practice though.
There are many good makers out there, for different budget as well. I do not do free promotion, but I am sure you can ask someone on Facebook.
Buy a sword suited for your physical structure. It should reach at least your neck. Better if it reaches your nose or if it equals you in height. Avoid swords heavier than 2,6 Kg more or less. If you think to hit targets or to do some kind of sparring with it, consider the opportunity to buy a sword with a Feder blade – aka a trainer, or waster – as you do not want to damage or to ruin a nice looking reproduction… or your friends. My first montante was a steel trainer.
I would suggest, with no doubt, three options: Ton Puey of Academia da Espada, Jan Gosewinkel of Montantero Bonn or III Montanteros in Malmö. Why don’t I put myself in? I spent more time on historical research, they are better trained than me, but in the future, who knows…