1-Is the fees on the legacy blockchain are more likely to get lower or higher in a near future? In others words, should I wait to do the transfer to a segwit address?
You are asking us to predict the future, which is impossible to do.
2-What kind a saving aprox. in % can I get from sending BTC from a segwit address to another segwit one vs a transaction done on the legacy blockchain?
For a one input, one output transaction, a segwit transaction will cost ~1/3 less than the analogous non-segwit transaction.
Since there is no rush, the best thing for you to do is to just send the transaction with a very low fee rate and with RBF enabled and then just wait for it to confirm. If it is taking too long, you can then bump the fee since you have RBF enabled. Otherwise just rebroadcast the transaction occasionally and wait a few days.