Help on a 2nd All Grain brew

Hi Guys,

I've brewed a bunch of extract kits which has turned out really nice, started with a couple mangrove jacks, coopers and then a WilliamsWarn kit which has been the best so far. The last kit is when I experimented with a bit of mini-mash - I added 200g of Special B Belgian Malt, 30g of Coriander seeds and 20g of Orange Zest - steeped for 15 mins, and added Brew Enhancer 20 the WW Extract kit. Heated for 10 mins, added it all to the fermenter and topped it off to 23l.

I was wondering about trying something similar with A.G. Methods. But I'm up against a few things:

No gas burner - have to do it all on an induction hob, so 30l pots are out of the question.

No 30l pot either - biggest one takes around 8-9l.

So here is my recipe and what i was planning to do was to make an 6-8l wort on the stove with grains, and hops etc, then top it up to 13-15l and make a smaller batch. In theory I could make this a 23l brew and top it up with unhopped LME (or as I've read a coopers lager kit after the boil - as they are pretty low in IBU's).

2kg - Gladfields Lager malt

1kg - Caramunich malt

500g - Wheat Malt

500g - Oats

250g - Dextrose - last 10 mins of the boil

100g - Maltodextrose - last 10 mins of the boil

Mash for 60 mins at 60C (BIAB - no sparging)
Wort would be around 6-8l while on the boil.

30g Styrian goldings hops (3.6% AA) - Boil for 60 mins

Cool wort to 23-24C and pitch Breferm Universal Yeast (6g)

I wanted to make something along the lines of a Belgian Tripel, but I prefer beers with a more orangey amber colour (hence the caramunich). Low IBU's and a sweeter malty flavour.

What are your thoughts on doing this and topping up the wort to 13-15l? Would that mean I would only get 35-40% efficiency?

Some online recipe calculators have said at that efficiency I should still be getting 6-7% ABV but I thought it would be less than that - maybe around 3%?