Unlike most highly pressurized tanks, those on the LM were generally cylindrical instead of spherical. It appears the cylinders had hemispherical end caps.

If you're going for something with a substancially higher propellant flow, then you'd be better off using larger tanks instead of using more tanks of the same size as Apollo's. For most geometric shapes, volume increases faster than surface area as you increase the size. Since the propellant tank's weight is proportional to the surface area, a larger tank is more efficient than several smaller ones.

For example, doubling the radius of a sphere increases its volume by a factor of 8 but the surface area (and therefore the weight) increases by a factor of 4.

For a given radius R:

Surface Area ~ 12.57R^2
Volume ~ 4.189R^3

Likewise, for a cylinder, doubling the radius increases the volume by a factor of 4 while the surface area meerly doubles.

Surface area = 2PI*height
Volume = PI * R^2 * height

Interestingly enough, according to this source, the J-series LMs used for Apollos 15-17 featured lengthened tanks to hold more propellant.

Four descent engine propellant tanks lengthened by 8.6 cm providing 521.5 kg extra fuel and oxidizer. Descent engine burned for longer period; combustion chamber modified to reduce erosion; expansion skirt modified.

LM Descent Stage cutaway

It'd probably be a reasonable idea to start with the old LM descent engines and upgrade them to be reusable. I've read that the old engines had erosion problems during development. You could either build bigger engines derived from that upgraded design or perhaps use multiple engines instead of one.

Tom is right about weight being a limiting factor with large pressurized tanks. If you want to build a more efficient engine, you'll need higher combustion chamber pressures. However, those higher pressures mean you need stronger (heavier) tanks to withstand the greater stress. Turbopumps allow for more efficient designs but at higher expense, greater complexity, more opportunities for failure, and perhaps a more difficult time throttling the engine quickly. Turbopump design is much more advanced than it was in the 1960s but the throttling and reliability issues might argue against it for a lander engine.

Hypergolic propellants were used on the Apollo SM and LM because of reliability and storability issues. They're used on the Shuttle OMS engines and attitude control thrusters for the same reason.