> I wanted to ask whether it is ok for me to start giving him some chicken, fish, liver, egg, cucumber etc as treats or tidbits
You've had some very good advice about this already but one thing I would suggest is you decide, with your family, just what you are feeding treats for. They are perfect as a reward and as part of your general training routine. but do not be tempted to feed tidbits from your plate, from your food prep areas or just because your puppy looks cute!! The latter will create bad habits in a dog that follows you and your plate around, and one that will steal when given the opportunity.
If this is your first dog have a look at
The Puppy Primer by Patricia McConnell - it's an excellent book for experienced and novice owners alike that helps to keep your training, and your puppy, on the straight and narrow.