This is the first of two paragraphs... my comments back to the student are in brackets; I post my edit as a comment to the student's blog post and then record the grade in my PowerGrade online gradebook.
His rebus adducti et auctoritate Orgetorigis permoti constituerunt ea quae ad proficiscendum pertinerent comparare, iumentorum et carrorum quam maximum numerum coemere, sementes quam maximas facere, ut in itinere copia frumenti suppeteret, cum proximis civitatibus pacem et amicitiam confirmare. Ad eas res conficiendas biennium sibi satis esse duxerunt; in tertium annum profectionem lege confirmant. Ad eas res conficiendas Orgetorix deligitur. Is sibi legationem ad civitates suscipit.
Persuaded [you got the participles; good job!] by these events and moved deeply by the clout/authority [good -- 'clout' is really the sense of 'auctoritas', though it is often translated as 'authority'] of Orgetorix, they prepared to gather what they needed to be sent out onto the field [they began gathering the things they'd need], to buy the greatest number of mules and carts [in English you can render better by putting -ing on that infinitive: 'buying as many mules and carts as possible'], to do a large amount of planting ['facere' has a broad semantic range: try 'sowing' (think about using an English word that describes better the 'making/doing' being expressed in 'facere')], in order to have enough/sufficient supplies for their journey, and to confirm peace and an alliance with the citizens [in this context, likely 'tribes'] close by. Two years was enough for these things to be led [I'd like you to reconstrue this sentence -- let's go over in class]; in the third year, they confirmed their motion of departure [lege -- 'by law' or 'by decree']. Orgetorix was chosen [nice, you got the passive correct] to prepare these things. He undertook the mission of the citizens upon himself. [Again, bring this up in class; we'll reconstrue together]
In addition, by blogging all of this, the student gets to keep a record of the Tweet-transcript, the final draft, my edits, and the grade on the assessment.
Come preparation for the final exam, the student will be able to go over a record of everything done in class by reviewing the blog. This is beneficial in two ways: first, there is no need for me to reinvent the wheel and handout end-of-the-year review sheets because, in effect, the students have been creating their own reviews throughout the year on their blogs. Second, rather than get a review sheet that reads like a page from a textbook, the students are actually able to review from their own work and work they've collaborated on with fellow students. The result is that student draw not just on prior knowledge, but on prior experience.
The blog itself is essentially a record of experiences interacting with the content of the course.