T
1. Taking a class every 2 levels is not a nerf.
2. Sure balance the classes for taking away free Cantrips, i.e. give the class an additional Skill or something.
3. The casting time is relatively easy to incorporate, it is already in the DMG under Speed Factors - include it for all so its a balance across the classes.
4. Replace the loss of spell foci with benefit - when casting a spell, gain +1 bonus on all rolls for an hour as the residue magical energies course through you.
As an example.
The fact that I disagree with your approach doesn't affect your using it in any way. Your group is not mine, and you do you.
It's also worth noting that my group and I don't use the optional multiclassing rules anyway, so the every-other-level approach isn't something we would do in the first place. We DID use the feat progression from one of the playtest packets, which builds off the Magic Initiate feat, and that worked OK. It's not too dissimilar.
I actually really like the way cantrips work in 5e, and have no issue with them in S&S games. My only issue with cantrips are the damage-dealing ones, which I generally ban or alter. Of course, if we enforce a multiclassing approach - either through actually multiclassing or the feat tree I used - characters have plenty of at-will damage options anyway and the damage cantrips become less relevant anyway.
We used speed factors in my games, and it worked. Of course, I am a big fan of the speed factors, having started in the 2e days, and my players were all new to D&D as of 5e, so I probably liked it more than them. But nobody complained, and it allows for greater tactical buildups so it was cool.
I also have no issue with spell foci, actually, since a spell focus can be damaged or stolen. Losing a spell focus provides good meat for roleplaying and quest directions, and while it might slow a caster down it certainly doesn't cripple them. As long as a caster requires tools of some kind to cast their spells, I feel it works.
But again, do whatever makes the game fun for your group. It's your game.