Eald Englisc to Niwum Englisce

All right, I suspect that's wrong; annoying language.

Which is, of course, why I'm thinking of working on creating a new
language based on Anglo-Saxon.

Some questions:

Why do we say /gIv/ instead of /yIv/?  It comes from giefan, which was
pronounced like /yievan/.

Why did we choose to change cg -> dg, sc -> sh, thorn -> th, and ae -> a?

What caused the vowel shift?

To vowels tend, in most languages, to become more open, more closed,
longer, shorter, midder, backer, forwarder?  :)

How does this look for a typical noun format?

ship

nom     ship            shipas
gen     ships           shipa
acc     ship            shipas
dat     shipe           shipum

This would hold true for most nouns (even those that don't follow the
paradigm in OE, like "hond" and maybe even "man," but I doubt it -- man
will probably be irregular:

man             men
mans            menna
man             men
men             mennum

Then we'd have the definite article

nom     se      the
gen     the     the
acc     thon    the
dat     thom    the