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1. Did Frederick II actually sent his troops to America to join up with his military advisor sent to help Washington to create his Continental Army there (And is this also affected Early American military uniforms to have Prussian appearances?)?
Wrong on both counts. First, because the famous "von Steuben" who wrote the first US Army drill manual and trained Washington's troops was something of a Con Man: he wasn't a general, only a Captain in the Prussian Army, and he was neither a Baron nor even a nobleman - he added the 'von' to his name himself. Frederick didn't prove of rebellions, but he also didn't approve of the British hiring mercenaries all over Germany (not just from Hessia) and driving up the price of his own mercenary hires, so he taxed the movement of British mercenaries through his provinces in Germany as if they were cattle - which made him more money, cost the British a bit more, and showed his opinion of the British practices. No Prussian military units were ever sent to America, not was it contemplated, unless the British thought they could hire Prussian units - not an unlikely idea, since the British and Dutch had 'hired' most of the Prussian Army back in 1702 - 1714 during the War of the Spanish Succession. BUT since Prussia was not on particularly good terms with any of its neighbors having just fought France, Austria, and Russia in the Seven Year's War, Frederick was not about to let any of his troops go adventuring in North America.
The American uniforms did not particularly look like Prussian uniforms - they looked like everybody in Europe's uniforms, and everybody in Europe was copying elements of the Prussian 'style' because the Prussian Army was considered, man for man, one of the best in Europe. The Americans got old French Army uniforms, bought old uniforms elsewhere, and when they made their own dyed them whatever color was handy and Cheap. That meant that the Connecticut militia were in brown coats, using cheap vegetable dyes, while Virginia and Carolina troops were in blue, because Indigo Blue dye plants were the first major cash export crop out of the Carolinas - it was readily available, even if to the untrained eye it made them look like the other major dark-blue coated army in Europe - the Prussians.
2. Personally Bombard should be 'Late Medieval' siege choice. with this... either Mortar or Obusier (Are both weapons the same thing? Mortars didn't use wheeled carriage to move around but had to be manhandled onto either wagons or rafts (Depending on transport conviniency) or elephants (if applicable) or pack horses or asses or mules (in case of Coehoorns).
Obusier is French for 'Howitzer'.
Mortars in the west first show up at the Siege of Constantinople in 1453 CE (the Korean
Wan'gu or "gourd-shaped mortar" is first mentioned about 1407 CE, so there are earlier Unique Mortars in Korea), so Mortar is really a Renaissance weapon, and pretty strictly a Siege weapon until after the howitzer became popular in the 18th century, when the howitzer began to take over the mortar's function - had the same ability to 'lob' shot over obstacles and walls, but longer range and better mobility. The US Civil War (1861 - 65 CE) was about the last major use of siege mortars, by 1905 CE in the Russo-Japanese War heavy howitzers were used in the same situations (Siege of Port Arthur)
You have to be careful here, because the only difference between a siege mortar and a siege howitzer is that the mortars generally were not on wheeled carriages, and technically, they have shorter barrels than a 'true' howitzer. That means you had 'mortars' in WWI and even WWII in the 20th century on wheeled carriages that are actually Howitzers in disguise: The German army in both wars, for instance, used a
21cm Morser that was actually a big howitzer.
3. Then if 'Siege Rifle' (did they call rifled siege cannons this way?) deserves the place as a separate unit to exists with rifling and comes before Artillery. then i'd say, in Vanilla and RF rule (mod potential, and i've yet to decide the proper design since this Parrot looks more like a field gun rather than siege gun) this weapon needs Iron to make. right? What do you think of James rifle cannon upgrades?
They used the term Siege Artillery for any guns considered too heavy to maneuver with the infantry (or cavalry). So, for instance, Parrott were made in 10 and 20 lb sized that were Field Artillery, and 100, 200, and even 300 lb that were Siege Artillery (and also some 'in between' weights that were Naval artillery) - all sizes refer to the weight of shot fired: the 300 lber was a 10" cannon or 253mm by modern measurement.
Parrotts, like the more popular 3" Ordinance Rifle (US Army) were made from Iron, as was the 1861 Krupp cast steel rifled guns, which were muzzle-loaders but so popular they were sold to not only the Prussia/German armies, but also the Ottomans, Austrians, and Russians in the 1860s. Between 1859 and 1866 Krupp had developed a breechloading system (also used by the French) that had an effective gas seal (but was not particularly effective for heavy guns) so in 1870 CE the FrancoPrussian War was fought by the Prussian/German Army entirely with rifled breechloading 75mm and 87mm Krupp guns.
The James system was one of many 'dead-ends' in the development of rifled, breechloading, quick firing field artillery in the 19th century. It put rifling grooves into the side of the cast iron shell to 'engage' the rifling in the barrel. This meant it cost more to make each shell, but also that the harder cast iron wore down the bronze barrels so fast it turned it into, effectively, a smooth bore in a short time. James system was tried by both the Union and Confederate armies in the US Civil War, and by 1862 (less than 2 years!) both sides were phasing them out as simply unusable for any length of time. They fall into the same category as the early breechloaders, most of which had serious gas leaks, or 'odd' rifling systems like the Whitworth or Armstrong guns, none of which lasted long.
-70
melee strength, and cost ~ 380
and 20 niter.
before spouting off weak info... Just wanted to mention to OP that mortars also existed at the time, and suggest proper stats for game balance. 
