1. Clematis have many different species and varieties with different flowering habits and different pruning requirements. If bought from a reputable supplier, it should have a label telling you what it is called, and what pruning regime to follow. Good idea to keep the label. Usually require about 3 years in the ground before they flower very much. If it is the kind that flowers on this year's growth, it will flower in late summer. If it is the kind that flowers on old wood, it will flower next year. If it is the kind that does both, it will do both. And there are many other kinds.

3. It's a Callistemon, which come in many different species and varieties. If bought from a reputable supplier, it should have a label telling you what it is. Good idea to keep the label. Looks like frost damage to me, though it could be too much/too little water. The different varieties have different frost hardiness, less reputable suppliers fail to point out that many are pretty marginal here. Where I live, we had some fairly harsh frosts in March, and it is precisely those late frosts that do the greatest damage. Best to protect with fleece at this time if it is one of the less hardy types. It will replace those dead leaves, but will have been set back by the damage. If you don't want the bother of protection, choose a hardier variety like Callistemon subulatus (which yours definitely isn't, 'cos C subulatus has narrow leaves). Despite being Australian, they do need plenty of water, naturally growing in areas with a good water supply. Given the weather this year, I doubt it is drought that is the problem, though it could be drowning if it is waterlogged.

5. It's called garlic mustard and is a wild plant, or weed if you like. The leaves can be used sparingly in salads when they are new.

2 and 4. Could be all sorts of things. If bought from a reputable supplier, it should have a label telling you what it is and how to look after it. Good idea to keep the label. Houseplants have individual requirements and many potential problems. Definition of houseplant - a dying plant whose certain death you are trying to delay. If you are interested in growing them, it is worth having a fat book or two about them. That will tell you how to look after each kind in much more detail than the label, and address the many kinds of problems they can have.