Well.....
It depends how many mortices you want to cut and in what size oak. I have a heavy duty chain morticer. They are quick but they are also scary. Personally I think they are best for through mortices or anything deeper than about 3 inches. I have tried every variation really on cutting mortice holes, including routers and auger bits. Most of the time I use a spade bit and chisel, with a 3lb Thor hammer for M&T joints.
Frankly, for doing tenons, everyone thinks they can take the timber to the bandsaw. You very quickly realise this is a daft idea and what you need is to take the tools to the oak. I cut all tenons with a big circular saw. Hilti in my case. Everyone does unless the are making frames in a barn or factory. If you can get your hands on a 12" Makita circular saw, or one of the US ones, that will speed things up no end. I also dimension beams this way. You quickly get adept at doing four cuts with a Circular saw to cut beams to length (rotating 9o degrees), with each cut meeting the next.
You only need one good big slick.
Invest in leather 3 lb and 5lb Thor hammers with iron heads. Brilliant. You night need a 10lb and 15lb hammer, but you can make these out of tree trunk off cuts (like everyone else). Good for encouraging frames to fit
Save yourself a LOT of work and get a big hand held planer. This will save you loads of time. Search my threads on the big (and cheap) Triton one, plus get a big 4" Makita sander with lots of 40 grit belts.
Think about raising the timbers. If you can afford hydraulic machinery, great. Otherwise start looking nor for big, second hand, tripod cranes.
Make or buy plenty of heavy duty trestles. But chain morticing is best done on blocks close to ground level. Chain mortices are heavy.