The PZ IV F1 is the last PZ IV to be equipped with the short barrel. It differs from its predecessors by several improvements: The armor is increased to 50mm, the tracks are widened, the tension roller is modified, the side hatches of turret are with two doors, the upper hull front plate becomes again rectilinear and the system of fixing of the machine-gun is improved.
At the origin the designation was ausf F, and not F1 But in the course of production, the OKH asked to equip the new PZ IV with the long barreled  7.5cm L43, more effective on the T34.  This new series will take the name of F2 (and will turn later in ausf G), the F becoming F1. The PZ IV F1 was Produced to 462 units, from April 1941 to March 1942. 

The Hasegawa model shows its age and seems outdated since the arrival of other productions on the market. It was nevertheless the only plastic model of PZ IV F1 at 1/72 for a long time. 
The main problem of the Hasegawa kit, the very bad vinyl tracks will go directly to the garbage bin, and will be replaced by a better hard plastic set from an old Esci kit. 
The EP set is from Eduard, the Preiser figure. 

the PZ IV ausf J will not cease to evolve and this kit presents a late version of it, which does not constitute an improvement of the engine, but a simplification in order to save resources and production time.  In August 1944, the exhaust pipe was replaced by two flame suppressors. In September, as on all the machines, the zimmerit is not applied any more and the schurzens of Thomas type, made up of grid, replace the plates of side armorings of body. 

In October, the system of opening of the trap door of the tank commander is modified: from now on it opens horizontally, like on the Panther or the Tiger II. The traction hooks at the front are now simplified and consist of an extension of the side armour plate of the chassis. Finally, in December, in order to reduce production time, one of the four return rollers is removed and a new hook is mounted at the rear of the body to allow the use of a tow bar.

The "Sturmpanzer IV Stupa" is an assault cannon intended for infantry support, based on the Panzer IV chassis and used by the Wehrmacht
The "Stupa" is wrongly designated "Brummbär", this error being due to problems of comprehension of the German appellations by the services of intelligence of the Allies.  Conceived at the beginning of 1942, it is a question of adapting a superstructure with thick armor (100 mm on the front, 50 mm on the sides), sheltering a howitzer of 150 mm resulting from the SIG 33, on a chassis of Panzer IV. Production began in May 1943 and continued until March 1945. A total of 298 Sturmpanzer IV were built

The Trumpeter kit is fancy, incomplete and not even at the level of quality one can expect today. The kit will nevertheless be improved, and will represent a hypothetical machine, supposedly based on a late Ausf J chassis. So, it's just ucronyism, as much as the decoration, based on the kit's manual and not on a picture of a real Stupa.

The 8.8 cm PaK 43 (L/71) auf Geschützwagen IV (Hornisse then Nashorn) was developed as an intermediate solution in 1942 to respond to the appearance of new Soviet tanks such as the T-34 and was armed with the powerful 88 mm gun whose anti-tank role had been demonstrated. The total production of the Hornisse and Nashorn amounted to 494 vehicles, most of which were built in 1943, although production continued until 1945. The Nashorn was delivered to the schwere Panzerjäger-Abteilungen (heavy anti-tank battalions), six of which were eventually equipped with 30 Nashorns, namely the schwere Panzerjäger Abteilungen 560, 655, 525, 93, 519 and 88. 

The Revell Kit was used to replicate the Nashorn. It is a good kit that needs no comment and has been assembled without major modifications, except for some over-detailing. Dragon has also released a Nashorn kit of comparable quality.

Following requests of armoured units for an anti-aircraft weapon capable of Following  armoured vehicles on all terrain, it was decided to produce an armoured vehicle carrying the new 3.7cm flak 43 L/60 on a PZ IV chassis.  Production began in early 1944 at the Krupp-grunson factories. In April 1944, the first 20 units were produced and joined their units. Production continued until March 1945, despite mobelwagen was considered as a temprary solution before the arrival of other flakpanzers better designed to their anti-aircraft role. Between 250 and 240 machines were built and joined armoured units  mainly on the western front.
The PZ IV hull is not fundamentally altered. The casemate is enlarged, the pilot's and radio stations fully closed and equipped with horizontally sliding hatches to allow the opening without being hindered by the shield of he gun. 

The machine gun is removed and replaced with a simple firing port
The gun is installed in the central compartment protected by a shield and folding panels allowing a medium-altitude or low-altitude shot, or even against ground targets, when the panel are totaly opened. This is the main defect of the Mobelwagen: In  road position (fully raised panels) or anti-aircraft fire at medium altitude (half-down panels) it has a very high silhouette that makes it an easy target and earned it its nickname of môbelwagen "moving van". In low-level firing position or against ground targets, the panels are completely lowered, and a part of the  crew is no longer protected. Another feature: A device, connecting the rear panel to the antenna, allows for the drop when the panels are lowered