Now the dilemma of what lens to go for? It takes Sinar boards and smaller Linhof ones. A 300 seems natural but this will mostly be for landscapes where wider might be better.
If you are looking at 300mm Lenses all the standard F5.6 Plasmats are good however they are all in copal three and by no stretch of the imagination could be called small. If you want compact looh for a Nikon M300 F9 this is a Tessar design in a copal 1 it has no where near the coverage of a plasmat and just covers 10x8 alternatively there is the Fuji C300 or A300 none of these are likely to be as usefull as a Sironar or Symar S but are quite a bit smaller and now often tend to cost more (when new they cost less than the Plasmats but now people want them as long lenses on 5X4.
Wide angles on 10x8 tend to cost more as landscape use is one of the few areas where 10x8 is still in some use your 35mm 35mm equivalentish is a 240mm none of the standard plasmats are all that special here with regard to image circle and are all in Copal three shutters the stand out lens is the Apo Sironar S with a 372mm image circle at F16 this is what I use I also have a 240mm Symar S but I find that it's image circle is insufficient for my needs other contenders are the rare and sort affer Fuji 250mm F6.7 W this is in copal 1 and has a simular image circle to the Apo Sironar.
210mm is your sort of 28mm 35mm equivalent and here again the choices are limited as no standard 210mm F5.6 Plasmat covers 10x8 however most of the manufacturers for a short time offered 80 degree plasmats, the Apo Sironar W and the Super Symar HM both offer about 350mm of coverage and are fairly rare and expensive the options if you need a wider image circle are true wide angle designs here there is the Super Angulon 210 F8 and the newer Super Symar XL F5.6 and the Grandagon N F6.8 these are all rarer than rocking horse excrement expensive and even by my standards &&&&&&&ing huge the practical lens is the Fuji 210mm W from the late seventies it is a single coated 80 degree plasmat in a copal one it has an adequate image circle of 350mm, I brought mine for about £200 in 2009 it is very important to now exactly what you are looking for with this lens as over the years there has probably been about five or six 210mm Fuji's.
If you want to go wider the next step is a 150mm lens here all the designs are wide angle ones no plasmat at that focal length comes close to covering 10x8 the 35mm equivalent is around 21mm. The cheapest option is the Super Angulon 165mm F8 these are huge and generally £500 plus better options are the Grandagon N 155mm F6.8 the Nikon 150mm Sw and the Super Symar XL 150mm F5.6 all are huge and expensive (generally £1000 +) and moderately rare to see for sale the Super Symar gets some peoples vote for being brighter I went with the Nikon as I already had and liked the 120SW all these lenses have about 400mm of image circle so most likely more than your camera can use they also all will need a centre filter if you are shooting slide film this in itself is likely to cost another £200 or so.
If you want wide still then there is the Nikon 120mm F8 SW its in copal 1 so not utterly huge but not exactly small either it has just enough image circle to cover 10x8 on a carefully centered camera but no movements (in practice whack it down to F32 and you can get away with a small amount of tilt. None of the other lenses in this range truly cover 10x8 and again you are going to be seaching for an expensive centre filter and I do mean searching as Nikon never made centre filters for their lenses and the 77mm filter thread of the Nikon is not shared with any Schneider or Rodenstock lenses at least that I'm aware off, the options are Heliopan (no longer available new) or Hoya did make a filter in this size as did Marumi or Fuji Gx617 filter for the 90mm lens I have both the Fuji and the Heliopan.
There are a few other wide angle options if you want to mess about with classic American "Glass" there is a Wollensack around 159mm I believe and some Ektar lenses that are useable older Angulons really are not and if you want to look into truly bizzare there is the Hypergon none of these will perform as well as any of the plasmats / wide angles mentioned above but some people seem to enjoy playing with them.
Ultimately what suits you is dependent on what you can manage to drag about with you / your budget / what is available.
As to MrCad go there in person if you can and speak to the owner Alex Falk especially with regard to large format gear. I to find a lot of their items over priced but then again I just buy stuff that I know is reasonable and also run off quickly with bargains if you know what you are about there are always some to be found. Alex himself is incredibly helpful if you get to know him and the shop provides a valuable service in having available just about everything you are ever likely to need albeit at a price some times.
No love for the Velvia 50 ? I'm amazed any is left at that price and not having a quickload is no excuse as they are dime a dozen now (well should be yours for say £15)
As a simple recommendation if I didn't have one already I'd have clicked the buy it now on
this instantly, the inside lettering means it is the 80 degree one with 350mm image circle.