Recommendations for modest budget

Two questions for the OP:
1) Do you mind used equipment?
2) Do you need 4K Video?

AVRs become obsolete quickly and have very little resale value.  The market for non 4 K AVR is infinite and you can probably get a great piece for virtually nothing .If you insist on 4K you can supplement it with something like Apple TV as a source and as a music streamer to boot.  A decent BRP can be had for under $100.  That would leave the bulk of your budget for a Speaker/Sub combo, or again you might be able to score big in the used market here.  The upgrade as funds allow

Amp power required depends upon Speaker characteristics, primarily impedence and sensitivity.  Keep in mind that that a low watt amp may sound fine most of the time but struggle with sudden increases in demand, either with music or with video.  Also keep in mind that power ratings for AVRs can be misleading, as manufacturers tend to sum what is delivered in each channel and report that number, so a 50 watt AVR may truly be 25 watts, for example, in 2 channel.  I once had a slimline Marantz AVR rated at 50 watts and it sounded awful and clipped easily.