First mini-mash performance anxiety and a Beta-Glucanase Rest

So I have everything for the BYO Oatmeal Stout coming in the mail within the next few days and I'm looking forward to my first attempt at a mini-mash.

Here's the Current Recipe
6 lbs. light dry malt extract
1 lb. crystal malt, 60¡ Lovibond
1.5 lb. American six-row pale ale malt
1.5 lb oatmeal (this is about 10%, I may bump to 15-20%)
0.5 lb. chocolate malt
0.5 lb. roasted barley
1/2 tsp. Irish moss, for 15 min.
2 oz. Fuggles hop pellets (4.2% alpha acid), for 45 min.
Wyeast 1084, Irish ale yeast

What I'm confused about is whether I can replace some of the DME with 2-row to lower my cost, and further my journey towards AG bliss.

By my understanding, I take the sum of my specialty grains (1.5+1.5+.5+.5)=4lbs and add an amount of 2-row to replace an equal amount of DME. So in this instance I would probably try to eliminate 3 lbs of DME and add 4.5 lbs of 2-row (that should get my back to the desired OG if my conversion skills are correct). Does that sound right? Or should I just stick with the DME? (although it's quite a bit more expensive than 2-row, and I could save it for my next brew)

Second part, I might pump up the oats, since they are a nutritious and delicious addition. Since that would require a Beta-Glucanase rest, I want to make sure I understand what that's going to "look" like. Since this is performed before the mash, can I add water and grains to my kettle, hold at 120 F for 30 minutes, then dump the whole mess in my mash tun and add enough water to hit 155 F and start my mash?

Thanks in advance.

I say stick with the DME, mini mashes are notoriously inneffecient in sugar extraction. Since the buld of your fermentable are coming from the DME, you should be able to hit your targe OG dead on that way.

Also, you can do the beta glucanase rest right in your MLT. Infuse with enough hot water to stabilize at 120*F, then when you are ready infuse with boiling water to hit your mash temp. That way you eliminate the hassle of trying to transfer anything. FWIW, I don't think you will need a b-glucanase rest unles you havae a TON (I would say worry about it if you get above 20%) of oats.

Good luck on your first partial buddy!

I've had very good success with mini-mashes, always within one or two points of the expected gravity. Your calculations are good for the DME/2-row replacement, but I would not go over 10% with the oats without adding some rice hulls (about 1/3 as much hulls as oats). The 6-row will convert itself and help with the oats, so you could go with less 2-row.