Hi Janet,
yes you're correct ref Bream Tufts. Re "Elwall", the usual best course for queries such as this is to search for old forum posts, and yes "Elwall" has been discussed/mentioned in the past and always wrt Bream area c1850ish.
Please see these prior threads, found by searching "Elwall";

http://forum.forest-of-dean.net/index.php?id=40812
http://forum.forest-of-dean.net/index.php?id=17692
http://forum.forest-of-dean.net/index.php?id=4071
etc

From these, plus as you say a lack of it's use on the first OS Maps (c1880 so still some 40 odd years after it's recorded use in Census') suggest to me that Elwall is an earlier spelling/pronounciation of Ellwood, no doubt influenced by the strong Vurrist dialect. Such apparent discrepancies around the Forest are quite common in the earlier Ordnance Survey maps, which were produced by Army surveyors from outside the Forest who presumably relied on locals for place names etc.

This site may also interest you wrt the Ellwood area http://www.4villages.org.uk/history

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And yes, I think you're probably correct wrt the location of Oakwood Mill, searching the forum will give several hits, this being perhaps the most usefull;
http://www.forum.forest-of-dean.net/index.php?id=16722
This usefull site suggests the original Oakwood Mill was a water mill.
http://theflourmill.com/about.html

However be advised that the whole Valley is called Oakwood, therefore I guess there could have been more than one Mill in the area over the centuries...
Re whether your ancestor resided IN the Mill in 1845, I guess the record might mean he lives NEAR it ?. Do you have any other records to suggest he did live there if not own it ?.
Also in case you didnt know there was an iron mine nearby which took the name Oakwood Mill Deep Level, it became part of the Princess Louise colliery.
http://www.sungreen.co.uk/_Bream/MillHill1950s.htm
http://www.copsewood.org/mining/books/oldham/fod_02.htm
http://www.derelictplaces.co.uk/main/showthread.php?t=8587

Ir seems thw earliest Oakwood Mill was a corn mill; this general history of corn mills in the Dean may hopefully be of interest;

"A mill built c1434 on Horwell hill (later Bream's Meend) by Richard Lawrence of Bream was demolished before 1623. It probably stood on a tributary, since disappeared, of Oakwood brook. The latter brook powered Oakwood Mill, a corn mill recorded from 1520 in a detached part of Newland. Another corn mill belonging to Newland was on the stream below Pope's hill at Blackmore's Hale, north-east of Littledean. It was acquired by the Heane family in 1659 and was evidently working in 1718. Its building was perhaps that used as a skin house in 1840.
By the mid 19th century the number of corn mills working in the Forest and at Lydbrook had increased. Waterloo Mill, on Greathough brook above Lydbrook, was on or near the site of the king's furnace of the early 17th century. The mill was operated by Thomas Burdock in 1841 and steam power had been installed by 1885. Downstream the Cooper family worked a corn mill at Newland bridge in Upper Lydbrook in 1841. A corn mill at the bottom of the valley, on the east side of the main street of Lower Lydbrook, belonged to the Highmeadow estate in 1792. In 1818 or 1819, when it was held by William Partridge, it was sold to James Pearce and in 1856 it was bought by Edward Russell. By the early 1820s it was held with nearby Gabbs Mill, to the south-east, which was worked in 1856 by the Little family.
Whitecroft had two corn mills in the early 19th century. One, on an eastern tributary of Cannop brook (or the Newerne stream), was known as Kidnalls Mill and was possibly in use in 1808. It may have been working in 1841. The other mill, on the west side of Whitecroft, stood at the end of a long race leading from Cannop brook in Whitemead park. It was worked by the Morse family by 1829 and had steam power in 1885. On Cinderford brook Thomas Brace converted a building below Cinderford bridge with an old water wheel, once used for drying coal, as a corn mill in 1818 or 1819. Moses Teague owned it and George Bright operated it in 1839. Downstream below Upper Soudley, at a wood turnery acquired in 1867 by Henry Crawshay, a new building was erected c. 1877 as a flour mill known as Camp Mill and a pond upstream of the site was enlarged. Shortly before 1846 a maltster, Timothy Bennett, built a steam-powered corn mill at a place known later as Steam Mills, north of Cinderford by the road and tramway to Nailbridge. Thomas Wintle worked it in 1856 and purchased it later, and in 1890 it passed with his Mitcheldean brewery to his son Francis.
Most of the corn mills were closed in the late 19th century or the early 20th. The mill in the main street of Lower Lydbrook was a paper factory in 1883 and for a number of years it made sugar paper for insulating detonator wire. Lydbrook's other corn mills ceased operating later, Waterloo Mill being used before 1912 to pump water to a nearby mine. Camp Mill at Soudley was used for millboard manufacture by 1888 and was sold in 1901 to James Joiner of Dulcote (Som.), who transferred ownership to his Dulcote Leather Board Co. The mill fell idle after the company went into receivership in 1908 and Joiner opened a saw mill there in 1922. That was closed c. 1952 and the site later became the premises of the Dean Heritage museum, opened in 1983. Oakwood Mill, which used steam power by 1885, closed c. 1900. Milling stopped at Cinderford bridge when the water supply there was reduced in the early 20th century and at Steam Mills before 1922. The mill in the west part of Whitecroft was abandoned in 1915 but by 1919 the Lydney and District Farmers' Co-operative Society had taken it over and it continued to operate it in 1970. The building was disused in 1992."
From: 'Forest of Dean: Industry', A History of the County of Gloucester: Volume 5: Bledisloe Hundred, St. Briavels Hundred, The Forest of Dean (1996), pp. 326-354.
URL: http://www.british-history.ac.uk/report.aspx?compid=23267
Date accessed: 12 July 2014.