Making a lemon pound cake with plain pound cake recipe.
I would use the zest of 2-3 lemons and maybe a teaspoon of juice. Lemon juice is very acidic, and too much will change the texture of your cake. (I know this from hard experience.)
I would use 1 tbsp. lemon juice and the grated entire rind of the lemon. The lemon flavor is largely in the lemon oil in the peel.
You probably don't need to add the juice. For a cake the size of a loaf, I use the zest of a whole lemon (or 1 tablespoon as my recipe states) ; if you are making a larger cake, you can probably increase this. When it comes out of the oven, poke holes with a toothpick and drizzle with a mixture of freshly-squeezed lemon juice mixed with sugar--delicious. Again for a loaf cake, I use 1/4 cup freshly squeezed and strained lemon juice and 1/3 cup sugar (for a more tart flavor I sometimes switch the ratios and use 1/3 cup juice to 1/4 cup sugar but I love tart flavors). Stir before pouring over the still- hot cake. For a ring cake or bundt increase accordingly. The ratios of lemon and sugar (above) are for a loaf-cake but make a generous amount of drizzle. For the loaf cake I cool 10 minutes on a rack then turn it out on the oiled rack (then flip it to cool right-side up). I haven't made this in a bundt, and understand cooling and turning out is more challenging, so for cooling and turning out advice, I defer to the bundt experts.