Your estrogen will be a little higher but so will your test levels, so you have a good balance there. Adverse issues are pretty much avoided by running it at low doses EOD as well towards the tail end. Negative mood impact from clomid generally doesn't appear when you're using lower dosages of clomid. More is not necessarily better in this case.
Because it blocks the estrogen receptor site in breast tissue so it can help prevent estrogen related gyno issues. However, if you have gyno symptoms already, letro is the way to go. Nolva can also be used after letro usage to prevent estrogen rebound (so you are trying to block the receptor sites in breast tissue from heightened estrogen levels from letro when the letro leaves your system after you stop use of it, which by the way you can alternatively just taper the letro dosage down to mitigate rebound as well, IMO the Nolva is handy to have in case you don't respond to the clomid treatment).
Clomid generally restores HPTA better though. It is the SERM that is recommended even in the relatively recent study on effective PCT protocols.