I'm sure it'll be a fine substitute, providing the SRM isn't too high. I use Gleneagles Maris Otter as my house base malt---the Gleneagles has an SRM around 3.5-4.5, a little higher than normal Maris Otter---but I like it that way---I think it's got more flavor than the normal MO. Anyway, check on the SRM just to be sure, but otherwise you should be just fine.
As to the percentage, that depends wholly on the style of beer you're brewing. Since it's a well-modified pale malt rather than an adjunct grain, you could use it for up to 100% of your grain bill if you wanted to, but again, it depends on the style. Personally, I've never used 100% of anything. My base malt makes up most of the bill, then I use a smaller percentage of adjuncts depending on the recipe.
MOSS HOLLOW BREWING CO.
Aristocratic Ales, Lascivious Lagers
•Scottish 80/- •Sweet Stout •Roggenbier
.primary | bright:
98: Moss Hollow Soured '09 72: Oude Kriek 99: B-Weisse 102: Brett'd BDSA 104: Feat of Strength Helles Bock 105: Merkin Brown
.on tap | kegged:
XX: Moss Hollow Springs Sparkling Water 95: Gott Mit Uns German Pils 91b: Brown Willie's Oaked Abbey Ale 103: Merkin Stout
98: Yorkshire Special 100: Maple Porter 89: Cidre Saison 101: Steffiweizen '09 (#3)