What time of year are you planning to travel? The northern Serengeti is great from July into August when the Migration is headed north into Kenya. Since you are considering Lemala camps in the Serengeti and Tarangire, you might also think about staying in their camp on the rim of the Ngorongoro Crater. They had a 7-day Migration Special using those 3 camps a while back and you'd most likely get a discount for booking all 7 nights with them. They could also coordinate all your transfers. Most Northern Circuit safaris go in the opposite direction, though... Tarangire, Ngorongoro, then the Serengeti (saving the best for last!)

While you might have better pricing in lodges off the Crater rim, you'll lose some of your early morning viewing time. It will take you an hour or more to get from the NCA gate into the Crater. If you're on the rim at the Lemala camp or the Ngorogngoro Sopa Lodge, you can be down in the Crater almost immediately. Take a picnic breakfast and take advantage of the best hour of game viewing. The Sopa is fairly reasonable and is next to a descent/ascent road. If you're staying off the rim, I'd recommend the Ngorongoro Farmhouse, my favorite.

In the northern Serengeti, we stayed at the Serengeti Mara Camp. At the time, it was the only one in the Lemai Wedge, tucked up against Kenya's Masai Mara (only without the crowds.) We saw a couple of wildebeest crossings on the Mara River.

October trip.

How much $$ are you saving by staying away from the crater rim? Not worth the trade-off IMO.

Are you going in this direction to make use of the Zanzibar to Kogatende flight as your only internal flight?

If you started in Tarangire after flying from Zanzibar, you'd probably need another flight back from the Serengeti.

Concur with spending a few more $$ to stay on the Crater rim not only for view, great sunset (depending on location) but also travel time. If this is first safari than strongly suggest staying on the rim.

End Oct is good to start at No. Serengeti, but know of the camps mentioned, Serengeti Mara will likely be the most expensive. However, even if considering less vehicles here, if like this year with lots of rain you might get stuck on that side of the river and transport to/from airstrip might be challenging, if possible. Any of the other camps mentioned should be considered and bearing in mind there are only 5-6 camps in the Kogatende area... not really an issue with too many vehicles. Admittedly, more control on the Serengeti side than in the Mara.

Forget the drive from Kogatende thru Central to the crater... will take almost a full day. Departing by air at about 10:30am to Lake Manyara, here met by guide/driver and vehicle for a transfer (about 2/hrs) to the Crater Rim* for stay overnight (Sopa good and priced right) so you can have early morning crater tour (these limited to 6/hrs officially). Then departing for drive about 3/hrs to Tarangire and when concluding stay here... drive to JRO for homebound.

Staying in Karatu, it will be at minimum a 1.5-2/hr drive to Crater, entry processing takes about 30/min depending on number of those waiting... then transit across Rim to descent road... probably not down on floor till 8am earliest! Why waste the 2/hrs?