(Partial answer - and a bit long winded)
Regarding comparable telescopes - source : The Herschel Objects and How to Observe Them, by James Mullaney.
Herschel's telescopes far surpassed in both quality and size any other telescope in the world at the time. After comparative trials at a number of observatories in England including Greenwich, he stated with confidence "I can now say that I absolutely have the best telescopes that were ever made."
His fame as a telescope maker spread rapidly and soon he was flooded with requests from both other observes and obervatories to make instruments for them. While he was not in
the telescope-making business as such, his allowance from the King – while freeing
him from his musical duties – did not entirely meet his expenses, and so he began
to make and sell telescopes privately. In addition to at least 60 complete instruments
(most of them 7- and 10-feet in size), he also made several hundred mirrors upon
order in addition to those for his own telescopes!
Curiously, Herschel thought he was observing a comet rather than a planet. From Harvard site:
Herschel's observations of the outline of the image on April 6 (perhaps a night with exceptionally good seeing) led him to remark, "the comet appeared perfectly sharp upon the edges and extremely well-defined without the least appearance of any beard or tail." This observation, however, seems not to have made him doubt that his object was a comet.
Two years after his initial observations, Herschel wrote in Philosophical Transactions, 73, 1, 1783 (quoting from the same Harvard article) :
Sir - By the observations of the most eminent astronomers in Europe, it appears that the star which I had the honour of pointing out to them in March 1781 is a Primary Planet of our Solar System.
Unfortunately Herschel does not name these astronomers, nor does he describe how they made their observations. However, Bode, who ultimately named Uranus, may not be amongst them. According to this article on the Messier.org site, Bode's role may have been that of collecting the observations of other astronomers. Bode names Mayer and Flamsteed as having observed Uranus prior to Herschel :
Bode was greatly interested in the new planet discovered by William Herschel in March 1781. While Herschel always referred to this planet as "Georgium Sidus" to honor King George III of England, and Messier called it "Herschel" or "Herschel's Planet," and Peitnet de Sevoy, "Cybele," Bode proposed the name "Uranus," which was soon adopted by the rest of the world. Bode collected virtually all observations of this planet by various astronomers, published many of them in the Astronomisches Jahrbuch, and found that Uranus had been observed before its discovery on a number of occasions, among them an observation of Tobias Mayer from 1756, and earliest by Flamsteed, in December 1690, cataloged as "star" 34 Tauri.
Regarding Lexell, you appear to be correct in stating that he did not perform direct observations. From the St. Andrew's Site :
When William Herschel discovered a new body in the solar system on 13 March 1781, Lexell computed its orbit which showed that it was a planet (later named Uranus) twice as far from the sun as Saturn, rather than a comet as had been thought at first. Although he did not predict the position of Neptune, as did Adams and Le Verrier, Lexell's initial calculations of the orbit of Uranus showed that it was being perturbed and he deduced that the perturbations were due to another more distant planet.
