Seagull TLR for landscape photos?

I tend to prefer the 6 x 7 or 6 x 9 formats for landscape photography,
but that's just my rectangular preference in those shots. If you want
to use 6 x 6 TLR, see if your budget will support a used Mamiya TLR
(C220/330). They're heavy, but they do have interchangeable lenses
ranging from 55mm to 250mm which will allow you to add wide angle or
telephoto capability later on should you desire it. No, add on lenses
don't really do the job. The Mamiya also has available for it a wide
range of focussing screens and viewing hoods/prisms, some metered. If
you can't swing a Mamiya C, a Rolleicord (I'd recommend V or, if you
get lucky on price, a Vb which would allow you the flexibility to
change format to 645 or other and which will accept interchangeable
viewfinders [standard chimney and eyelevel pentaprism]), an Autocord
(Minolta), or a Diacord or Ricohmatic 225 (Ricoh) should do it nicely
for you. Some people also will suggest a Yashica, but I've had
reliability issues with each of the ones I've owned. The reliability
of any camera, of course depends on how well it is treated and
maintained.

A down side to using TLRs is that they do not have through the lens
metering with any configuration so if yuou use filters or polarizers,
you will need to remember to make adjustments in your f-stop or speed
to compensate for the light loss. You will also not be able to view
the effect of your polarizer or filter unless you first put it on the
viewing lens and then move it down to the taking lens. A Minolta
Autopol is handy since it allows you to see and adjust the degree of
polarization. It has two linked filters one over the viewing lens and
the other over the taking lens. It is, however, uncommon and expensive
unless you get lucky. The Rolleicords, Ricohs, Yashica, and Minolta
all take Bayonet 1 filters. The Mamiya lenses generally take either
46mm or 49mm although some earlier lenses use a different size. You
can get adapters to use 49mm accessories on your Bay 1 camera. This is
important since 49mm filters tend to be more plentifiul and thus easier
to obtain and often less expensive than Bay 1