Help with planning a cable run for data cables

[ban-all-sheds]

That's going to be fun, with all that protrusion into the box, with a lot of fittings you'll find that things just don't fit. I generally use white oval - for the simple reason that in this house, the brick is so 'kin hard (and the mortar soft) that chasing anything else in is going to be "difficult". I use nibblers to expand the knockouts so that I can get the end of the conduit flush with the inside face of the box - and no more.

Cheap they are not, unless you get lucky on fleaBay, but these MK Masterseal conduit entries are great:

Virtually no protrusion in the box, and for the users of oval conduit, as they are soft you can squeeze them between finger and thumb, the opening becomes oval, and the oval conduit slips in. No more having to hack the box about.

 

[SimonH2]

If you use the smaller oval, you don't need those - they just fit in the 20mm knockouts.
Try getting a 3<something>mm white oval (the biggest one) into one of those AND still be able to use the full capacity of the conduit. I hit capacity for the largest white oval just the other day - 3x WC/WF100 coax, one Cat5e, one CW1308. Wanted another Cat5e in there but it just wasn't going to go (in hindsight, should have put 2 conduits in but before plans changed I couldn't see any chance of one not being enough !) The whole point of taking the end of the conduit into the box without any adapters and stuff is that you have a straight and smooth run without anything to obstruct the cables.
And I'd not call it "hacking" the box about to just nibble the knockout into a slot that'll take the oval.