Where is the ‘head’ on infested chargers

Both mods have an effect on Paris (I have yet to acquire the other two) and they work exactly how you described them. Quotes from the Paris wiki page:

• Reload speed mod increases the speed at which arrows are drawn from the quiver after each shot.
• Fire rate mod increases the draw speed of the Paris, allowing you to charge an arrow much quicker.

Yes, it possible to do so. Though, it's really not recommended due to the resource costs involved.

To make (or access) the dojo itself, you must first create or join a clan. Then someone needs to make the Clan Key (the blueprint of this will be added to the player's foundry once they join a clan). The resources required are the following:

• 1 Morphic
• 500 Polymer Bundle
• 500 Ferrite
• 1500 Credits
• 12 Hours to build

Afterwards, the basic Clan Dojo, with a basic Clan hall as the starting room, is created. Now, resource costs for building other rooms (connectors, reactors, research facilities, etc.) are scaled depending on what clan size bracket you fall into (in this case, your supposed clan will fall into the Ghost Clan bracket - 1-10 members in total).

Yet still, they are quite expensive for a small number of players to handle, especially due to the usage of "rare" resources at higher levels (such as Forma). Unless you have a large stockpile of resources and credits, it's suggested to have at least 4-6 members to build a basic dojo with the important facilities. But, it's certainly doable with 1-2 people, though not recommended.

I strongly suggest you pay a visit to the Warframe wiki page on Clan Dojos for more information on each room type's costs, as well as for pre-planning the layout. Remember, you don't want to waste resources destroying and creating more rooms than necessary!