Are you going to form your Troops for the time before 1632?
Tercio's are pretty hard to 'form' because of their Massive appearance. What you are certainly know
If you estimate the size of Imperial Tercio's for 1618 -1632 as about 4000 Men each gives a lot of Miniatures and a pretty Massive Block. One way or another you'll have to decide in which Figure Men Ratio you gonna build your Force. After that you can consider the Type of Bases to use and how you are downsizing them if need should be.
I go with my Saxons on 1:20, Netherland Ordinance, which still leaves me with 120 Figures/Regiment
Basing for Musketeers 8x9 Figure Bases (3x3) and 6x8 Figure Bases (2x4) for the Pikes.
That enables me to enlarge but also decrease the unit Size without loosing the General Formation Proportions.
For a Tercio...2400-4000 Men Strong well if you go for 180 Miniatures that gives about 80 Musketeers and 100 Pikemen
For the Musketeers would therefore the 4 Figure Base and the Pikes in even sided Block Front and Depth.. 10x10 Figure Bases(2x5).
Similar for Swedish Brigades...as it can be broken up into Smaller Bodies like detached Musketeers I would go for 4 Figure Bases to provide the necessary flexibiilty for them.