hey if you have knowledge, are eager for the experience and do the research there is no reason not to go allgrain, i have only done 3 kits and on my third also did an all grain brew at the same time. there are mini mash brews you could consider also to start you off, specialty grains, hops, boil time and mashing just smaller scale and a little help from liquid/dry malt extract to cut down the grain bill.
all that aside you sound like you are a man of conviction and have pretty much set your self on the path of AG so i say to you good luck and welcome to the hobby, im sure you will have no problems.
water levels appear more complicated than they actually are, some of the info you need wont be available to you untill you have your brewing gear; mash efficiency, Hot liquor tun/Mash tun/boiler dead space for instance. stuff like hop water absorption and grain absorption can be pretty well calculate from online info.
many people have different methods, i got all in a spin on my brew but just opted for a 50/50 split, i calculated with all the above in account i needed 37 liters in total to reach an end result of 23 liters in the fv, i did a 18.5 liter 60 minute mash and 18.5 liter 10 minute batch sparge and it seemed to work just fine for me, i say this with jest as i broke my hydro so have no OG and boiled for too long before starting my hop addition @ 60 minutes so ended with a 90 minute boil, i had to add 2 liters of water at the end to bring to volume but the extra boil time didn't have hops in so wont effect the final goal for the beer, i cant chart my efficiency as i didn't get an OG but my wort was uber sweet and uber tasty so i have no worrys and think i was not too far off.
best advice i can give you is now you have done some reading just go for it!